wit

(noun): (now usually in the plural) Sanity.
(noun): (obsolete usually in the plural) The senses.
(noun): Intellectual ability; faculty of thinking, reasoning.
(noun): The ability to think quickly; mental cleverness, especially under short time constraints.
(noun): Intelligence; common sense.
(noun): Humour, especially when clever or quick.
(noun): A person who tells funny anecdotes or jokes; someone witty.

He's gone completely out of his wits.
Where she has gone to is beyond the wit of man to say.
My father had a quick wit and a steady hand.
The opportunity was right in front of you, and you didn't even have the wit to take it!
The best man's speech was hilarious, full of wit and charm.