The Collaborative International Dictionary of English v.0.48:
Stallion \Stal"lion\ (st[a^]l"y[u^]n), n. [OE. stalon, OF. estalon, F. ['e]talon, fr. OHG. stal a stable. See Stall, n.] A male horse not castrated; a male horse kept for breeding. [1913 Webster]WordNet (r) 3.0 (2006):
stallion n 1: uncastrated adult male horse [syn: stallion, entire]