gill arch vs gill bar

gill arch and gill bar both are nouns.

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

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

gill arch and gill bar: 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 branchial arch.

gill arch (noun)	gill bar (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