railyoudaoicibaDictYouDict[rail 词源字典]
rail: English has three words rail. The oldest, ‘rod, bar’ [13], comes via Old French reille ‘iron bar’ from Latin rēgula ‘straight stick, rod’, source of English regular and rule. The bird-name rail [15] goes back via Old Northern French raille to Vulgar Latin *rascula, which probably originated in imitation of the bird’s hoarse cry.

And rail ‘complain, be abusive’ [15] comes via Old French railler ‘mock’ and Provençal ralhar ‘scoff’ from Vulgar Latin *ragulāre ‘bray’, an alteration of ragere ‘neigh, roar’. This in turn was a blend of Latin rugīre ‘bellow’ and Vulgar Latin *bragere ‘bray’ (source of English bray [13]). Raillery [17] and rally ‘tease’ [17] come from the same source.

=> regular, rule; bray, rally[rail etymology, rail origin, 英语词源]
rail (n.1)youdaoicibaDictYouDict
"horizontal bar passing from one post or support to another," c. 1300, from Old French reille "bolt, bar," from Vulgar Latin *regla, from Latin regula "straight stick," diminutive form related to regere "to straighten, guide" (see regal). Used figuratively for thinness from 1872. To be off the rails in a figurative sense is from 1848, an image from the railroads. In U.S. use, "A piece of timber, cleft, hewed, or sawed, inserted in upright posts for fencing" [Webster, 1830].
rail (n.2)youdaoicibaDictYouDict
"small wading bird," mid-15c., from Old French raale (13c.), related to râler "to rattle," of unknown origin, perhaps imitative of its cry.
rail (v.1)youdaoicibaDictYouDict
"complain," mid-15c., from Middle French railler "to tease or joke" (15c.), 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.
rail (v.2)youdaoicibaDictYouDict
"fence in with rails," late 14c., from rail (n.1). Related: Railed; railing.