The Collaborative International Dictionary of English v.0.48:

hipbone \hipbone\ n.
   Either of two large flaring bones, each forming one half of
   the pelvis; made up of the ilium and ischium and pubis.

   Syn: innominate bone.
        [WordNet 1.5] Hipe

WordNet (r) 3.0 (2006):

hipbone
    n 1: large flaring bone forming one half of the pelvis; made up
         of the ilium and ischium and pubis [syn: hipbone,
         innominate bone]