weaken vs countermine

weaken is not a noun while countermine is a noun.

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

As verbs, weaken and countermine are synonyms defined as:

Other synonyms of weaken include counteract, sabotage, subvert, undermine.

weaken (noun)	countermine (noun)
	(military) a tunnel dug to defeat similar activities by the enemy

weaken (verb)	countermine (verb)
become weaker	destroy enemy mines with one's own mines
lessen the strength of	destroy property or hinder normal operations
reduce the level or intensity or size or scope of
lessen in force or effect
destroy property or hinder normal operations