bout (n.)
1540s, from Middle English bught, probably from an unrecorded Old English variant of byht "a bend," from Proto-Germanic *bukhta- (see bight (n.)). Sense evolved from "a circuit of any kind" (as of a plow) to "a round at any kind of exercise" (1570s), "a round at fighting" (1590s), "a fit of drinking" (1660s).