The Collaborative International Dictionary of English v.0.48:
Spritsail \Sprit"sail\ (spr[i^]t"s[=a]l; among seamen spr[i^]t"s'l), n. (Naut.) (a) A sail extended by a sprit. (b) A sail formerly hung under the bowsprit, from the spritsail yard. [1913 Webster]WordNet (r) 3.0 (2006):
spritsail n 1: a fore-and-aft sail extended by a sprit