A tachyon or tachyonic particle is a hypothetical particle that always moves faster than light. The word comes from the pronounced tachy , meaning rapid. It was coined in 1967 by Gerald Feinberg. The complementary particle types are called luxon (always moving at the speed of light) and bradyon (always moving slower than light), which both exist. The possibility of particles moving faster than light was first proposed by O. M. P. Bilaniuk, V. K. Deshpande, and E. C. G. Sudarshan in 1962, although the term they used for it was "meta-particle".