When something attenuates, it lessens in size or intensity; it becomes thin or weakened.

A behemoth is monstrously large in size or power; sometimes it’s given a negative implication in the sense that a behemoth is so large that it is difficult or impossible to manage.

If something daunts you, it makes you worried about dealing with it because you think it will be very difficult or dangerous.

Debility is the state in which you are physically or mentally weak, usually because of an illness.

Decrepitude is the state of being very old, worn out, or very ill; therefore, something or someone is no longer in good physical condition or good health.

A despot is a leader who has a lot of power and uses it in a cruel and unreasonable way.

Someone who is diffident is shy, does not want to draw notice to herself, and is lacking in self-confidence.

A dilapidated building, vehicle, etc. is old, broken-down, and in very bad condition.

When one person eclipses another’s achievements, they surpass or outshine that person in that endeavor.

If you describe a person, group, or civilization as effete, you mean they are weak, exhausted, powerless, unproductive, and/or corrupt.

Efficacy is the ability or power to produce an expected effect or result.

A person or animal that is emaciated is extremely thin because of a serious illness or lack of food.

If someone is described as feckless it means that he is incompetent and lacks the determination or skill to achieve anything in life.

If something is formidable it is impressive in size, power, or skill; it can make you feel frightened, alarmed, or in awe because it is so powerful or difficult to deal with.

Something that is gargantuan is extremely large.

Something that is immutable is always the same and cannot be changed.

An impregnable opinion or feeling is very difficult to change.

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

An indomitable foe cannot be beaten.

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

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

Something that inhibits you from doing something restricts or keeps you from doing it.

You describe someone as inimitable, especially a performer, when they are so good or unique in their talent that it is unlikely anyone else can be their equal.

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

A juggernaut is a very powerful force, organization, or group whose influence cannot be stopped, especially when it is large and powerful and will likely have bad effects.

A leviathan is something that is very large, powerful, difficult to control, and rather frightening.

If you refer to an organization or system as a monolith, you mean it is very large and unwilling or very slow to change and adopt something new.

If you have a nemesis, it is an opponent or archrival whom you cannot beat or is a source of ruin that causes your downfall.

Numinous objects or places seem holy, spiritual, and possess a mysterious power, which make you feel that a spirit or god may be present.

A plenipotentiary is someone who has full power to take action or make decisions on behalf of his or her government in a foreign country.

Something’s potency is how powerful or effective it is.

A potentate is a ruler who has great power over his people.

Something that is prodigious is very large or impressive and great.

If you describe someone as redoubtable you have great respect for her, although you may be afraid of her as well.

A skittish person or animal is easily made nervous or alarmed and is likely to change behavior quickly and unpredictably.

A stricture is a rule or condition that imposes restrictions or limits on what you can do.

If you surmount a problem or difficulty, you get the better of it by conquering or overcoming it.

Something tenuous is thin, weak, and unconvincing.

To be timorous is to be fearful.

Something that is transcendent not only surpasses all others in quality, achievement, or significance, but exceeds normal limits or boundaries.

Someone is tremulous when he or she is shaking slightly from nervousness or fear, or is simply afraid of something.

Something that is trivial is insignificant, commonplace, of little value, or not important.

A thing or person that is unremitting is persistent and enduring in what is being done.

If you are unsurpassed in your field of study, you are the best—period.

The zenith of something is its highest, most powerful, or most successful point.