gill arch vs branchial arch

gill arch and branchial arch both are nouns.

Word	Noun	Adjective	Verb	Adverb
gill arch	Yes	No	No	No
branchial arch	Yes	No	No	No

As nouns, gill arch and branchial arch are synonyms defined as:

gill arch and branchial arch: one of the bony or cartilaginous arches on each side of the pharynx that support the gills of fishes and aquatic amphibians

Other synonyms of gill arch include gill bar.

gill arch (noun)	branchial arch (noun)
one of the bony or cartilaginous arches on each side of the pharynx that support the gills of fishes and aquatic amphibians	one of the bony or cartilaginous arches on each side of the pharynx that support the gills of fishes and aquatic amphibians