When you are adept at something, you are very good, skillful, or talented at it.

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

A bailiwick is a person’s sphere of knowledge or learned skill.

A bravura performance, such as of a highly technical work for the violin, is done with consummate skill.

The caliber of a person is the level or quality of their ability, intelligence, and other talents.

If someone shows consummate skill at doing something, that person’s skill is very great or almost perfect in every way.

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

Debility is a state of being physically or mentally weak, usually due to 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 deft movement or action is made quickly and with skill.

If you describe someone, usually a young woman, as demure, you mean that she is quiet, shy, and always behaves modestly.

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

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

Someone who is feckless is incompetent and lacks the determination or skill to achieve much of anything at all in life.

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

A languid person is slow, relaxed, and shows little energy or interest in doing anything.

Lassitude is a state of tiredness, lack of energy, and having little interest in what’s going on around you.

If you are lethargic, you are tired, lack energy, and are unwilling to exert effort.

When you are listless, you lack energy and interest and are unwilling to exert any effort.

Malaise is a feeling of discontent, general unease, or even illness in a person or group for which there does not seem to be a quick and easy solution because the cause of it is not clear.

Someone’s mettle is their courageous determination and spirited ability to deal with problems or difficult situations.

Someone is obtuse when they are slow to understand things; someone can choose to be obtuse when they deliberately do not try to figure things out.

Something is quintessential when it is a perfect example of its type.

When you have been remiss, you have been careless because you did not do something that you should have done.

A sagacious person is wise, intelligent, and has the ability to make good practical decisions.

A savant is a person who knows a lot about a subject, either via a lifetime of learning or by considerable natural ability.

If your body is affected by torpor, you are severely lacking in energy; therefore, you are idle—and can even be numb.

A virtuoso is someone who is very skillful at something, especially playing a musical instrument.