in cheers, 1870, a shortening of hurrah. Adjective rah-rah is attested from 1907, originally indicating college life generally, later enthusiastic cheerleading.
early 15c., "mounted military expedition," Scottish and northern English form of rade "a riding, journey," from Old English rad "a riding, ride, expedition, journey; raid," (see road). The word fell into obscurity by 17c., but it was revived by Scott ("The Lay of the Last Minstrel," 1805; "Rob Roy," 1818), with a more extended sense of "attack, foray, hostile or predatory incursion." By 1873 of any sudden or vigorous descent (police raids, etc.). Of air raids by 1908.
"one engaged in a hostile or predatory incursion," 1863, agent noun from raid (v.). A word from the American Civil War.
"horizontal bar passing from one post or support to another," c. 1300, from Old French raille, reille "bolt, bar," from Vulgar Latin *regla, from Latin regula "rule, straight piece of wood," diminutive form related to regere "to straighten, guide" (from PIE root *reg- "move in a straight line").
In U.S. use, "A piece of timber, cleft, hewed, or sawed, inserted in upright posts for fencing" [Webster, 1830]. Used figuratively for thinness from 1872. By 1830s as "iron or steel bar or beam used on a railroad to support and guide the wheels." To be off the rails "out of the normal or proper condition" in a figurative sense is from 1848, an image from railroads.
"complain, speak vehemently and bitterly," late 15c., railen, from Old French raillier "to tease or joke" (15c.), which is perhaps from Old Provençal ralhar "scoff, to chat, to joke," from Vulgar Latin *ragulare "to bray" (source also of Italian ragghiare "to bray"), from Late Latin ragere "to roar," probably of imitative origin. See rally (v.2). Related: Railed; railing.