branchial arch vs gill arch

branchial arch and gill arch both are nouns.

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

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

branchial arch and gill 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 branchial arch include gill bar.

branchial arch (noun)	gill 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