Meaning of “counter” - Learner’s Dictionary

counter

verb [ T ] uk us /ˈkaʊntər/
PREVENT

to prevent something or reduce the bad effect that it has:

This skin cream claims to counter the effects of sun damage.
REACT

to say something to show that what someone has just said is not true:

"Of course I love him," Clare countered.

(Definition of “counter verb” from the Cambridge Learner’s Dictionary © Cambridge University Press)