a hypothetical non-Newtonian repulsive component of the force of gravity, postulated as an addition to the four known fundamental forces (gravitational, electromagnetic, strong, and weak)
fifth force in American English
noun
a theoretical force in nature in addition to the strong and weak forces, gravitation, and the electromagnetic force
Word origin
[1975–80]This word is first recorded in the period 1975–80. Other words that entered Englishat around the same time include: bench press, gridlock, noogie, retrovirus, surrogate mother