to act or avail against with equal power, force, or effect; counteract.
2.
to furnish an equivalent of or a compensation for; offset.
3.
Archaic. to equal.
–verb (used without object)
4.
to be of equal force in opposition; avail.
Origin: 1350–1400; ME contrevailen < AF countrevail-, tonic s. (subj.) of countrevaloir to equal, be comparable to < L phrase contrā valēre to be of worth against (someone or something). See counter-, -valent
[koun-ter-veyl] 
tərˈveɪl