(1):

(n.) A strip of wood or iron fastened on transversely to something in order to give strength, prevent warping, hold position, etc.

(2):

(n.) A device made of wood or metal, having two arms, around which turns may be taken with a line or rope so as to hold securely and yet be readily released. It is bolted by the middle to a deck or mast, etc., or it may be lashed to a rope.

(3):

(v. t.) To strengthen with a cleat.