This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

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v. To oppose and mitigate the effects of by contrary action; check.

v. To act in opposition to; to hinder, defeat, or frustrate, by contrary agency or influence; as, to counteract the effect of medicines; to counteract good advice.

v. To act in opposition to; to hinder, defeat, or frustrate, by contrary agency or influence.

To act in opposition to; hinder, defeat, or frustrate by contrary agency.

Synonyms To thwart, check, contravene, cross, neutralize.

v. act in opposition to

v. oppose and mitigate the effects of by contrary actions

v. oppose or check by a counteraction

v. destroy property or hinder normal operations

"Another influence we have to counteract is that of newspaper headings and placards which catch the eye of children in the streets and appeal so powerfully to their imagination."

counteracted    counteracting    counteractively    counteracts   

act    move    control    check    contain    hold    moderate    hold in    curb   

counterpoise   

counteracted    counteracting    counteractingly    counteractively    counteraction    counteracter    counteractant    counteractive    counteractor   

destroy    oppose    nullify    cancel    neutralize    correct    frustrate    hinder    impede