The Collaborative International Dictionary of English v.0.48:

Jennet \Jen"net\ (j[e^]n"n[e^]t), n. [F. genet, Sp. jinete,
   orig., a mounted soldier, Ar. zen[=a]ta a tribe of Barbary
   celebrated for its cavalry.]
   A small Spanish horse; a genet.
   [1913 Webster]

WordNet (r) 3.0 (2006):

jennet
    n 1: female donkey [syn: jennet, jenny, jenny ass]