rein: [13] A rein is etymologically something that ‘retains’. It goes back via Old French rene to Vulgar Latin *retina, a descendant of the Latin verb retinēre ‘hold back’, from which English gets retain and retinue. The rein for horses has no connection with the rein- of reindeer [14], incidentally; that comes from Old Norse hreinn ‘reindeer’, which may be of Lappish origin. => retain, retinue[rein etymology, rein origin, 英语词源]