countermine vs undermine

countermine is a noun but undermine is not a noun.

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

As verbs, countermine and undermine are synonyms defined as:

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

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

countermine (verb)	undermine (verb)
destroy enemy mines with one's own mines	hollow out as if making a cave or opening
destroy property or hinder normal operations	destroy property or hinder normal operations