pelvic arch vs innominate bone

pelvic arch and innominate bone both are nouns.

Word	Noun	Adjective	Verb	Adverb
pelvic arch	Yes	No	No	No
innominate bone	Yes	No	No	No

pelvic arch (noun)	innominate bone (noun)
the structure of the vertebrate skeleton supporting the lower limbs in humans and the hind limbs or corresponding parts in other vertebrates	large flaring bone forming one half of the pelvis; made up of the ilium and ischium and pubis