Quick Summary

Prefixes are key morphemes in English vocabulary. The prefix in, which means “in, on, or not,” appears in numerous English vocabulary words, for example: inject, influx, and insane. Prefixes do tend to have different meanings, which can be divined by context, common sense, and the process of elimination.

Prefixes and the Prefix "In"

Prefixes are key parts of English words. For instance, take the word prefix itself. Pre, which means “before,” is the prefix in the word prefix. Fix, which means “fastened,” is the “stem,” or primary part of the word. Thus, a prefix etymologically is that group of letters which is “fastened before” the stem of a word; that is, prefixes begin a word.

Today we will focus on the prefix in, which can mean “in, on, or not.”

Two highly used meanings of in are “in” or “on.” Let’s look at a few examples. In, for instance, can mean “in,” such as in the words inject, to throw “in,” and influx, to flow “in.” In can also mean “on,” used in such words as inscribe, to write “on,” and invoke, to call “on.” Hence, the first primary meanings of in are “in” or “on.”

The English prefix in can also, however, mean “not.” This is a trickier part of this prefix, but once you get the hang of it, it’s highly valuable in decoding English vocabulary. Some examples of in meaning “not” include insane, or “not” sane, independent, or “not” dependent, and invalid, or “not” valid.

By using common sense, context, or the process of elimination, you will find it easier to determine whether in means “in, on” or “not.” For example, inject, throw “in,” would make no sense as “not throw.” Conversely, the word insane makes little sense as “on” sane or sane “in;” rather “not” sane is the most obvious contextual choice.

In our next rootcast we’ll discuss the prefix in again, paying attention to its spelling changes as it attaches to various different stems. Just remember for now that in can mean “in, on, into or not,” and you’ll have this prefix mastered “in” no time at all!

  1. inject: throw ‘in’
  2. influx: flow ‘in’
  3. inscribe: write ‘on’
  4. invoke: call ‘on’
  5. insane: ‘not’ sane
  6. independent: ‘not’ hanging from something
  7. invalid: ‘not’ valid


  • intractable

    Intractable problems, situations, or people are very difficult or impossible to deal with.

  • inconspicuous

    Something that is inconspicuous does not attract attention and is not easily seen or noticed because it is small or ordinary.

  • intransigent

    An intransigent person is stubborn; thus, they refuse to change their ideas or behavior, often in a way that seems unreasonable.

  • innocuous

    Something innocuous is not likely to offend or harm anyone.

  • inimitable

    Someone, such as a performer or athlete, is inimitable when they are so good or unique in their talent that it is unlikely anyone else can be their equal.

  • insipid

    Something insipid is dull, boring, and has no interesting features; for example, insipid food has no taste or little flavor.

  • ineluctable

    Something that is ineluctable is impossible to avoid or escape, however much you try.

  • inexorable

    The adjective inexorable describes a process that is impossible to stop once it has begun.

  • incontrovertible

    Incontrovertible facts are certain, unquestionably true, and impossible to doubt however hard you might try to convince yourself otherwise.

  • indelible

    If someone leaves an indelible impression on you, it will not be forgotten; an indelible mark is permanent or impossible to erase or remove.

  • indiscreet

    Someone who is indiscreet shows lack of judgment, especially because they say or do things in public that should only be said or done privately—if at all.

  • incognito

    Someone who is going around incognito is using a false name and/or has changed their appearance in order not to be recognized.

  • inimical

    If someone is inimical, they are unfriendly and will likely cause you harm.

  • ineffable

    The adjective ineffable refers to something that is so impressive and beautiful that you cannot describe it in words.

  • interminable

    Something that is interminable continues for a very long time in a boring or annoying way.

  • intestate

    If someone dies intestate, they die without having made a will or legal document that explains who gets their money and property.

  • incongruous

    Something that is incongruous is strange when considered along with its group because it seems very different from the other things in its group.

  • ingrate

    If you describe someone as an ingrate, you are criticizing them because they do not express thanks to someone who has helped them—they are ungrateful.

  • indolent

    An indolent person is lazy.

  • indefatigable

    If someone is indefatigable, they never show signs of getting tired.

  • incommensurate

    One thing that is incommensurate with another is different in its level, size, or quality from the second; this may lead to an unfair situation.

  • inert

    When something is inert, it has no power of movement or is inactive.

  • incorrigible

    Someone who is incorrigible has bad habits or does bad things and is unlikely to ever change; this word is often used in a humorous way.

  • inestimable

    Something that has inestimable value or benefit has so much of it that it cannot be calculated.

  • insatiable

    If someone has an insatiable desire for something, they always want more of it and never feel as though they have enough.

  • infallible

    If something is infallible, it is never wrong and so is incapable of making mistakes.

  • inequitable

    If you say something is inequitable, you are saying that it is unjust because it is not equally fair for everyone.

  • intrepid

    An intrepid person is willing to do dangerous things or go to dangerous places because they are brave.

  • inscrutable

    Something inscrutable is very hard to figure out, discover, or understand what it is all about.

  • insouciance

    Insouciance is a lack of concern or worry for something that should be shown more careful attention or consideration.

  • inadvertent

    An inadvertent action is not done intentionally; rather, it is an accident that happens because someone is not being attentive to their surroundings.

  • inalienable

    An inalienable right is a privilege that cannot be taken away.

  • inanimate

    Something inanimate is dead, motionless, or not living; therefore, it does not display the same traits as an active and alive organism.

  • incessant

    Something that is incessant continues on for a long time without stopping.

  • incoherent

    Someone who is speaking in an incoherent fashion cannot be understood or is very hard to understand.

  • incommunicado

    If you are incommunicado, you are out of touch, unable to be communicated with, or in an isolated situation.

  • incompatible

    If two people are incompatible, they do not get along, tend to disagree, and are unable to cooperate with one another.

  • inconceivable

    Something that is inconceivable cannot be imagined or thought of; that is, it is beyond reason or unbelievable.

  • inconclusive

    If the results of something are inconclusive, they are uncertain or provide no final answers.

  • inconsequential

    Inconsequential matters are unimportant or are of little to no significance.

  • inconsolable

    Someone who is inconsolable has been so devastated by a terrible event that no one can help them feel better about it.

  • indifferent

    If you are indifferent about something, you are uninterested or neutral about it, not caring either in a positive or negative way.

  • indignant

    When you are indignant about something, you are angry or really annoyed about it.

  • indispensable

    An indispensable item is absolutely necessary or essential—it cannot be done without.

  • indomitable

    An indomitable foe cannot be beaten.

  • ineffectual

    Someone who is ineffectual at a task is useless or ineffective when attempting to do it.

  • inept

    Someone who is inept is unable or unsuitable to do a job; hence, they are unfit for it.

  • infamous

    An infamous person has a very bad reputation because they have done disgraceful or dishonorable things.

  • infinitesimal

    Something infinitesimal is so extremely small or minute that it is very hard to measure it.

  • infirmity

    A patient who is plagued by infirmity is weak in body or ill in health.

  • iniquity

    Iniquity is an immoral act, wickedness, or evil.

  • inopportune

    When something happens at an inopportune time it is inconvenient or not suitable.

  • integral

    Something that is integral to something else is an essential or necessary part of it.

  • invulnerable

    Someone or something that is invulnerable cannot be harmed in any way; hence, they or it is completely safe or secure.

  • invariable

    An invariable quantity is constant or unchanging.

  • inhospitable

    An inhospitable person is unfriendly or not very welcoming to another.

  • inevitable

    Something that is inevitable will certainly occur because it cannot be avoided.

  • infinite

    Something infinite has no end or any limits at all.

  • indeterminate

    When a piece of information is indeterminate, it cannot be known with certainty.

  • inconsistency

    An inconsistency is something that does not quite fit or disagrees somehow with the rest of the members of its group.

  • indubitable

    A conclusion or statement that is indubitable is certain, unquestionable, or true beyond the shadow of a doubt.

  • insuperable

    That which is insuperable, such as a barrier or challenge, is not able to be overcome, surpassed, or dealt with.

  • independent

    Someone who is independent takes care of themselves and does not rely on anyone to help them.

  • individual

    An individual thing is its own thing or is apart from other things.

  • invisible

    Something invisible cannot be seen.

  • inactivity

    the state of being inactive

  • inadequate

    lacking the requisite qualities or resources to meet a task

  • inculpable

    free of guilt

  • indolence

    inactivity resulting from a dislike of work

  • ineptitude

    unskillfulness resulting from a lack of training

  • infidelity

    the quality of being unfaithful

  • inglorious

    (used of conduct or character) deserving or bringing disgrace or shame

  • innumerable

    too numerous to be counted

  • insane

    afflicted with or characteristic of mental derangement

  • intolerant

    unwilling to tolerate difference of opinion

  • invalid

    force to retire, remove from active duty, as of firemen

  • inviolable

    incapable of being transgressed or dishonored

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