Buck1  —n. 1 male deer, hare, rabbit, etc. 2 archaic dandy. 3 (attrib.) Slang male. —v. 1 (of a horse) jump upwards with its back arched. 2 (usu. Foll. By off) throw (a rider) in this way. 3 (usu. Foll. By up) colloq. A cheer up. B hurry up; make an effort. [old english]