A reciprocal relationship.
A relation of mutual dependence or action or influence.
A reciprocal construction involves two noun phrases where each of the participants occupies both the role of agent and patient with respect to the other. see: Wikipedia:Reciprocal pronoun.
The characteristic of being reciprocal, e.g. of a relationship between people.
The mutual exchange of rights, privileges or obligations between nations. see: Wikipedia:Reciprocity (international relations).
The responses of individuals to the actions of others.
The cooperation of two or more nerves, muscles, organs, etc.
Benefits resulting from combining different groups, people, objects or processes.
A synonym of binding energy.
The combined action of two or more drugs where the effects are stronger than their mere sum.