If someone is quick-witted, their mind moves fast in the moment. They catch a joke while it is still in the air, see what a question is really asking, and find a smart answer before the room has gone quiet. People say it as a compliment, mostly about talk and small problems that need a fast thought — a meeting, a tease, a sudden change of plan — not about sitting with a hard book for hours. You can be deep and slow and still very clever; quick-witted is a different gift. It is everyday English, warm rather than stiff. Though actually, it is not the same as “funny”: a quick-witted person often makes people laugh, but the heart of the word is speed of understanding, not the job of being a clown. The opposite feeling is slow-witted or dim-witted, which can sound unkind, so we use those with care.