The Collaborative International Dictionary of English v.0.48:

Ovipositor \O`vi*pos"i*tor\, n. [L. ovum an egg + positor a
   placer, fr. ponere to place.] (Zool.)
   The organ with which many insects and some other animals
   deposit their eggs. Some ichneumon files have a long
   ovipositor fitted to pierce the eggs or larvae of other
   insects, in order to lay their own eggs within the same.
   [1913 Webster]

WordNet (r) 3.0 (2006):

ovipositor
    n 1: egg-laying tubular structure at the end of the abdomen in
         many female insects and some fishes