oral fissure vs oral cavity

oral fissure and oral cavity both are nouns.

Word	Noun	Adjective	Verb	Adverb
oral fissure	Yes	No	No	No
oral cavity	Yes	No	No	No

As nouns, oral fissure and oral cavity are synonyms defined as:

oral fissure and oral cavity: the opening through which food is taken in and vocalizations emerge

Other synonyms of oral fissure include mouth, rima oris.

oral fissure (noun)	oral cavity (noun)
the opening through which food is taken in and vocalizations emerge	the opening through which food is taken in and vocalizations emerge