facultative vs elective

facultative is not a noun while elective is a noun.

Word	Noun	Adjective	Verb	Adverb
facultative	No	Yes	No	No
elective	Yes	Yes	No	No

As adjectives, facultative and elective are synonyms defined as:

facultative (noun)	elective (noun)
	a course that the student can select from among alternatives

facultative (adjective)	elective (adjective)
able to exist under more than one set of conditions	subject to popular election
of or relating to the mental faculties	optional
granting a privilege or permission or power to do or not do something
optional