As nouns,
ornithischian dinosaur is a hypernym of
ornithopod dinosaur; that is, ornithischian dinosaur is a
word with a broader meaning than ornithopod dinosaur:
ornithopod dinosaur: bipedal herbivorous dinosaur
ornithischian dinosaur: herbivorous dinosaur with a pelvis like that of a bird
Other hypernyms of ornithopod dinosaur include
ornithischian.