The Collaborative International Dictionary of English v.0.48:

Hemimetabolic \Hem`i*met`a*bol"ic\, a. (Zool.)
   Having an incomplete metamorphosis, the larv[ae] differing
   from the adults chiefly in laking wings, as in the
   grasshoppers and cockroaches.
   [1913 Webster]

WordNet (r) 3.0 (2006):

hemimetabolic
    adj 1: (of an insect with aquatic young) undergoing incomplete
           metamorphosis in which the young does not resemble the
           adult [syn: hemimetabolous, hemimetabolic,
           hemimetamorphous, hemimetamorphic]