counteract vs countervail

counteract and countervail both are verbs.

Word	Noun	Adjective	Verb	Adverb
counteract	No	No	Yes	No
countervail	No	No	Yes	No

As verbs, counteract and countervail are synonyms defined as:

counteract and countervail: oppose and mitigate the effects of by contrary actions

Other synonyms of counteract include counterbalance, neutralize.

counteract (verb)	countervail (verb)
act in opposition to	oppose and mitigate the effects of by contrary actions
destroy property or hinder normal operations	compensate for or counterbalance
oppose or check by a counteraction
oppose and mitigate the effects of by contrary actions