fundamental interaction

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Any of the four most basic ways in which subatomic particles interact, comprising the strong, weak, electromagnetic, and gravitational interactions.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics any of the fundamental forces that act between elementary particles; each one is associated with an exchanged particle

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (physics) the transfer of energy between elementary particles or between an elementary particle and a field or between fields; mediated by gauge bosons