Counter-acting means to work against or neutralize the effect of something. There are many synonyms that can be used instead of counter-acting such as opposing, resisting, thwarting, hindering, impeding, obstructing, nullifying, negating, countering, balancing, undoing, mitigating, and offsetting. Each of these synonyms carries a unique nuance which can be used to express the same idea as counter-acting. For example, opposing could be used to emphasize active opposition while mitigating could be used to express the idea of lessening the effect of something. When choosing a synonym for counter-acting, it is essential to consider the context and the specific shades of meaning carried by those synonyms.