1918, so called about the time they became popular as aquarium fish, from the scientific name (Girardinus guppii), which honored R.J.L. Guppy, the British-born Trinidad clergyman who supplied the first specimen (1866) to the British Museum. The family name is from a place in Dorset. Other early popular names for it were rainbow fish and million fish. The class of streamlined U.S. submarines (1948) is an acronym from greater underwater propulsion power + -y.