To act against with equal force; counteract.
To compensate for; offset.
To act against an often detrimental influence or power.
To make up for; compensate.
To counteract; be successful, useful, etc. against; avail against.
(archaic) To match or equal.
To avail (against)
Origin of countervail
- Middle English countrevaillen from Old French contrevaloir contrevail- contre- counter- valoir to be worth (from Latin valēre to be strong wal- in Indo-European roots)
From American Heritage Dictionary of the English Language, 5th Edition