The Collaborative International Dictionary of English v.0.48:
Crossbow \Cross"bow`\ (kr[o^]s"b[=o]`), n. (Archery) A weapon, used in discharging arrows or bolts, formed by placing a bow crosswise on a stock. [1913 Webster]WordNet (r) 3.0 (2006):
crossbow n 1: a bow fixed transversely on a wooden stock grooved to direct the arrow (quarrel)