trigeminal vs trigeminus

trigeminal and trigeminus both are nouns.

Word	Noun	Adjective	Verb	Adverb
trigeminal	Yes	No	No	No
trigeminus	Yes	No	No	No

As nouns, trigeminal and trigeminus are synonyms defined as:

trigeminal and trigeminus: the main sensory nerve of the face and motor nerve for the muscles of mastication

Other synonyms of trigeminal include fifth cranial nerve, nervus trigeminus, trigeminal nerve.

trigeminal (noun)	trigeminus (noun)
the main sensory nerve of the face and motor nerve for the muscles of mastication	the main sensory nerve of the face and motor nerve for the muscles of mastication