unified field theory definition by American Heritage Dictionary
A physical theory that combines the treatment of two or more types of fields in order to deduce previously unrecognized interrelationships, especially such a theory unifying the theories of nuclear, electromagnetic, and gravitational forces.
Any theory in which two seemingly different forces are seen to be fundamentally identical. Maxwell's equations express a unified field theory that demonstrates the basic identity of electricity and magnetism, and the standard model postulates a basic identity for the strong force, the weak force, and electromagnetism.
A theory that unites and explains the basic forces of nature (strong, electroweak, and gravitational forces) as manifestations of a single physical principle. No unified field theory that has been proposed so far has gained broad acceptance.