contra-, contro-, counter, contre-

(Latin: against, opposed to, opposite, conflicting, different, clashing, unaccommodating)

counterclaim (s) (noun), counterclaims (pl)
A legal process designed to settle differences between two contesting parties over an issue as the consequence of a court action by one of the parties: Mr. Heller filed a counterclaim on behalf of his client in an effort to settle the conflict between his client and the neighbor over the issue of building a fence.
counterclaimant (s) (noun), counterclaimants (pl)
An individual or legal firm that initiates a court action to contradict the information filed by an opposing party: Justice Brown dismissed the appeal of the counterclaimant of the court's decision, stating that there was not sufficient information to warrant a new hearing.
counterclockwise, counter-clockwise
counterdemonstration (s) (noun), counterdemonstrations (pl)
A public display held in opposition to another public attitude or behavior: Some people in the city advocated that their country go to war while others had counterdemonstrations against any kind of military violence.
counterdemonstrator (s) (noun), counterdemonstrators (pl)
Someone who participates publicly in opposition to another display of feelings for or against something: David and Maurice were two of the couterdemonstrators protesting against those who want to do away with the university requirement that all students must take at least one year of Latin before they can earn their undergraduate degree.
counterespionage (s) (noun) (normally there is no plural)
A government's actions that are designed to detect, to hinder, or to prevent spying by agents of other countries; especially, enemies: Henry's uncle was involved in counterespionage against Germany in World War II and now some are saying that Germany is probably involved in counterespionage against their U.S. "friends".