(UK, Australia, New Zealand, South Africa, idiomatic, informal) To know; to be acquainted with (a person).

Alternative form of it takes one to know one

(idiomatic) To clearly understand one's own feelings, intentions, preferences, etc; to know precisely what one wants; to be decisive or determined.

(rhetorical question) Implies that a statement is based on a guess or assumption rather than on knowledge or evidence.

(colloquial, set phrase, rhetorical question, often sarcastic) What a surprise; guess what? / Used other than figuratively or idiomatically: see what, do, you, know.

(idiomatic) To have sex with someone.

present participle of know someone in the biblical sense

(intransitive, idiomatic) To be experienced and knowledgeable. / (transitive, idiomatic) To be very familiar with; to have a significant understanding of.

Alternative form of know which end is up

(idiomatic) To possess sound judgment or common sense; to have a clear understanding of a situation.