To reduce to obedience or discipline, tame, train (horses or other animals, also human beings); to subject or habituate to. Now also to break in…

transitive. To train or break in (a horse or other riding animal). Obsolete.

To mount, ride on (a horse); also, to break him in to the saddle. Also, figurative of the billows, etc. (Cf. To breast the waves.) Now rare.

transitive. To tame, train, or break in (an animal, esp. a horse).

transitive. To break in (a horse). Now rare.

transitive. North American. To tame or train (a horse). Cf. break, v. 14a.