branchial cleft vs gill slit

branchial cleft and gill slit both are nouns.

Word	Noun	Adjective	Verb	Adverb
branchial cleft	Yes	No	No	No
gill slit	Yes	No	No	No

As nouns, branchial cleft and gill slit are synonyms defined as:

branchial cleft and gill slit: one of a series of slit openings in the pharynxes of fishes and aquatic amphibians through which water passes

Other synonyms of branchial cleft include gill cleft.

branchial cleft (noun)	gill slit (noun)
one of a series of slit openings in the pharynxes of fishes and aquatic amphibians through which water passes	one of a series of slit openings in the pharynxes of fishes and aquatic amphibians through which water passes