(Britain, slang, derogatory) A person who annoyingly tries too hard to impress with their cleverness.

(slang) Somebody who is rather too clever; a smart aleck; sometimes used as an epithet.

(idiomatic, intransitive) To act wisely.

(idiomatic, of a person, plan, theory, etc.) Shrewd but flawed by overthinking or excessive complexity, with a resulting tendency to be unreliable or unsuccessful.