gill slit vs gill cleft

gill slit and gill cleft both are nouns.

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

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

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

Other synonyms of gill slit include branchial cleft.

gill slit (noun)	gill cleft (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