1. Zool.one of a series of bony or cartilaginous arches on each side of the pharynx that support the gills of fishes and aquatic amphibians; gill bar.
2. Embryol.one of a series of archlike mesodermal thickenings of the body wall in the pharyngeal region of the embryo of amphibians, reptiles, birds, and mammals. Also called gill arch, visceral arch.