(1):

(n.) Barter; exchange.

(2):

(n.) The arrangement of any determinate number of things, as units, objects, letters, etc., in all possible orders, one after the other; - called also alternation. Cf. Combination, n., 4.

(3):

(n.) The act of permuting; exchange of the thing for another; mutual transference; interchange.

(4):

(n.) Any one of such possible arrangements.