fundamental force

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

• noun Any of the four most basic forces that act on subatomic particles, comprising the strong, weak, electromagnetic and gravitational forces. In the fundamental interactions between subatomic particles, the fundamental forces act to change the state of motion of an existing particle, to destroy an existing particle, or to create a new particle.

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.