A young servant or follower; a military attendant.
Nowadays, a person on whom a knighthood has been conferred by a monarch.
(chess) A chess piece, often in the shape of a horse's head, that is moved two squares in one direction and one at right angles to that direction in a single move, leaping over any intervening pieces.
(card game) A playing card bearing the figure of a knight; the knave or jack.