coun ‧ ter ‧ vail ‧ ing /ˌkaʊntəˈveɪlɪŋ◂ $ -ər-/ BrE AmE adjective formal
[ Date: 1300-1400 ; Language: Old French ; Origin: contrevaloir , from contre- ( ⇨ ↑ counter- ) + valoir 'to be worth' ]
with an equally strong but opposite effect
coun ‧ ter ‧ vail ‧ ing /ˌkaʊntəˈveɪlɪŋ◂ $ -ər-/ BrE AmE adjective formal
[ Date: 1300-1400 ; Language: Old French ; Origin: contrevaloir , from contre- ( ⇨ ↑ counter- ) + valoir 'to be worth' ]
with an equally strong but opposite effect
Longman Dictionary of Contemporary English. Longman - Словарь современного английского языка. 2012