weaken vs alter

weaken and alter both are verbs.

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

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

Other hypernyms of weaken include change, modify.

weaken (verb)	alter (verb)
become weaker	remove the ovaries of
lessen the strength of	become different in some particular way, without permanently losing one's or its former characteristics or essence
reduce the level or intensity or size or scope of	cause to change; make different; cause a transformation
lessen in force or effect	insert words into texts, often falsifying it thereby
destroy property or hinder normal operations	make an alteration to