The Collaborative International Dictionary of English v.0.48:

gunsight \gun"sight`\ (g[u^]n"s[imac]t`), n.
   A sight[9] attached to a gun, used for aiming it at the
   target. Same as sight[9].
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

gun-sight
    n 1: a sight used for aiming a gun [syn: gunsight, gun-
         sight]