1. (n.) Intermediate action.

2. (n.) Mutual or reciprocal action or influence; as, the interaction of the heart and lungs on each other.

ESP alternation answer coaction commerce communication communion complementary distribution concurrence congress connection contact conversation converse cooperation correspondence dealing dealings engagement exchange information interchange intercommunication intercommunion intercourse interlacing intermeshing interplay intertwining interweaving interworking linguistic intercourse mesh meshing message quid pro quo reply response seesaw social intercourse speaking speech speech circuit speech situation talking telepathy tit for tat touch traffic truck two-way communication