coun·ter·vail 
(koun′tər-vāl, kountər-vāl′)
(koun′tər-vāl, kountər-vāl′)v. coun·ter·vailed, coun·ter·vail·ing, coun·ter·vails
v.tr.
1. To act against with equal force; counteract.
2. To compensate for; offset.
v.intr.
To act against an often detrimental influence or power.
[Middle English countrevaillen, from Old French contrevaloir, contrevail- : contre-, counter- + valoir, to be worth (from Latin valēre, to be strong; see wal- in the Appendix of Indo-European roots).]