"beam of light," c. 1300, from Old French rai (nominative rais) "ray (of the sun), spoke (of a wheel); gush, spurt," from Latin radius "ray, spoke, staff, rod" (see radius). Not common before 17c. [OED]; of the sun, usually in reference to heat (beam being preferred for light). Science fiction ray-gun is first recorded 1931 (but the Martians had a heat ray weapon in H.G. Wells' "War of the Worlds," 1898).