the world > animals > mammals > group Ungulata (hoofed) > family Equidae (general equines) > equus caballus or horse > [noun] > looked after in particular way (3)
a horse kept at pasture; (hence) a horse fed exclusively on grass.
A horse that is put up and fed. (Cf. board, v. 8b.)
Originally U.S. A horse which is (or has been) kept at livery. Also occasionally: an owner of such a horse.