11 letters · 13 points in Scrabble
noun a mutual or reciprocal action; interacting
noun (physics) the transfer of energy between elementary particles or between an elementary particle and a field or between fields; mediated by gauge bosons
originEtymology tree Medieval Latin interāctiōbor. English interaction Borrowed from Medieval Latin interāctiō.
Etymology from Wiktionary, CC BY-SA 3.0