Physics Any of four fundamental ways in which elementary particles and bodies can influence each other, classified as strong, weak, electromagnetic, and gravitational.
Main Entry: in·ter·ac·tion Pronunciation: "int-&-'rak-sh&n Function: noun : mutual or reciprocal action or influence<interaction of the heart and lungs> —in·ter·ac·tion·al/-shn&l, -sh&n-&l/adjective