(physics) the transfer of energy between elementary particles or between an elementary particle and a field or between fields; mediated by gauge bosons
make a counterattack and return like for like, especially evil for evil; "The Empire strikes back"; "The Giants struck back and won the opener"; "The Israeli army retaliated for the Hamas bombing"
diffusion of molecules through a semipermeable membrane from a place of higher concentration to a place of lower concentration until the concentration on both sides is equal