trepan vs trephine

trepan and trephine both are nouns.

Word	Noun	Adjective	Verb	Adverb
trepan	Yes	No	Yes	No
trephine	Yes	No	Yes	No

As nouns, trepan and trephine are synonyms defined as:

trepan and trephine: a surgical instrument used to remove sections of bone from the skull

trepan (noun)	trephine (noun)
a drill for cutting circular holes around a center	a surgical instrument used to remove sections of bone from the skull
a surgical instrument used to remove sections of bone from the skull

trepan (verb)	trephine (verb)
cut a hole with a trepan, as in surgery	operate on with a trephine