brighten vs alter

brighten and alter both are verbs.

Word	Noun	Adjective	Verb	Adverb
brighten	No	No	Yes	No
alter	No	No	Yes	No

As verbs, alter is a hypernym of brighten; that is, alter is a word with a broader meaning than brighten:

Other hypernyms of brighten include change, modify.

brighten (verb)	alter (verb)
make more cheerful through the use of color	remove the ovaries of
become clear	become different in some particular way, without permanently losing one's or its former characteristics or essence
	cause to change; make different; cause a transformation
	insert words into texts, often falsifying it thereby
	make an alteration to