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 quality or state of being simultaneous; simultaneousness.
More than one complete musical texture occurring at the same time. This first appeared in the music of Charles Ives, and is common in the music of Conlon Nancarrow, and others.