(idiomatic) A joke, especially one which strikes the listener or reader as particularly humorous.

Reaching up to the knees. / Submerged to the knees. / (figuratively, by extension) Deeply involved in something, or preoccupied with something.

Reaching to the height of a person's knees.

(chiefly in the plural) A sock that reaches almost up to the knee.

(slang) A casual outdoor sexual encounter (commonly with a prostitute), usually in an alleyway or against a wall, with the man standing and the woman's knees raised.

plural of knee sock

(US, usually in the plural) A sock or stocking that reaches to the knees; chiefly, women's nylon stockings that end slightly above the knee and supported by garter belts.

The medical condition genu valgum

Alternative spelling of knock knee

plural of knee-jerk