ornithischian vs ornithischian dinosaur

ornithischian and ornithischian dinosaur both are nouns.

Word	Noun	Adjective	Verb	Adverb
ornithischian	Yes	No	No	No
ornithischian dinosaur	Yes	No	No	No

As nouns, ornithischian and ornithischian dinosaur are synonyms defined as:

ornithischian and ornithischian dinosaur: herbivorous dinosaur with a pelvis like that of a bird

ornithischian (noun)	ornithischian dinosaur (noun)
herbivorous dinosaur with a pelvis like that of a bird	herbivorous dinosaur with a pelvis like that of a bird