trephine vs trepan

trephine and trepan both are nouns.

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

As nouns, trephine and trepan are synonyms defined as:

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

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

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