Synonyms for Counterblow:

n.

counteraction (noun)
an eye for an eye.
retaliation (noun)
reciprocation, counterattack, response, vengeance, reprisal, an eye for an eye, revenge, reparation, counteraction, retribution, return, retaliation.
revenge (noun)
reprisal.

v.

retaliate (verb)
exchange, redress, retaliate, reciprocate, return fire, reprise, retort, countercharge, avenge, Retribute, respond, counteract, repay, counter, revenge.
revenge (verb)
punish, restitute.

Other synonyms:

counterattack. requital, tit for tat. Other relevant words:
requital, like for like, an eye for an eye, counterattack, measure for measure, a tooth for a tooth.