na-adjective, noun
ready wit; quick thinking; improvisational cleverness
Describes the ability to respond cleverly and appropriately on the spot, often in conversation or performance. Can be used as a noun or adjectival noun.
彼の即妙な返答に、会場がどっと沸いた。
The audience burst into laughter at his quick-witted reply.
即妙の才がある人は、どんな場でもうまく立ち回れる。
A person with a talent for ready wit can handle any situation smoothly.
The word is composed of 即 (immediate) and 妙 (exquisite, clever). The exact historical derivation is uncertain, but the combination naturally conveys the idea of instant cleverness.