pelvic girdle vs pelvic arch

pelvic girdle and pelvic arch both are nouns.

Word	Noun	Adjective	Verb	Adverb
pelvic girdle	Yes	No	No	No
pelvic arch	Yes	No	No	No

As nouns, pelvic girdle and pelvic arch are synonyms defined as:

pelvic girdle and pelvic arch: the structure of the vertebrate skeleton supporting the lower limbs in humans and the hind limbs or corresponding parts in other vertebrates

Other synonyms of pelvic girdle include hip, pelvis.

pelvic girdle (noun)	pelvic arch (noun)
the structure of the vertebrate skeleton supporting the lower limbs in humans and the hind limbs or corresponding parts in other vertebrates	the structure of the vertebrate skeleton supporting the lower limbs in humans and the hind limbs or corresponding parts in other vertebrates