- The definition of countersue is when someone is suing you and you turn around and sue them.
When your neighbor sues you for trespassing and you sue your neighbor for encroaching on your land, this is an example of a time when you countersue.
transitive verbcoun·ter·sued, coun·ter·su·ing, coun·ter·sues Law
(third-person singular simple present countersues, present participle countersuing, simple past and past participle countersued)
- (intransitive) To sue a person or entity who is suing one.
counter- + sue