"to plait, knit, weave, twist together," c. 1200, breidan, from Old English bregdan "to move quickly, pull, shake, swing, throw (in wrestling), draw (a sword); bend, weave, knit, join together; change color, vary; scheme, feign, pretend" (class III strong verb, past tense brægd, past participle brogden), from Proto-Germanic *bregdanan "make sudden jerky movements from side to side" (compare Old Norse bregða "to brandish, turn about, move quickly; braid;" Old Saxon bregdan "to weave, braid;" Old Frisian brida "to twitch (the eye);" Dutch breien "to knit;" Old High German brettan "to draw, weave, braid"), perhaps from a PIE root *bhrek- (compare Sanskrit bhurati "moves quickly," Lithuanian bruzdùs "fast"), but there are phonetic difficulties. In English the verb survives only in the narrow definition of "plait hair." Related: Braided; braiding.
1817, "composed of two parts, double, twofold," from Latin duplex "twofold," from duo "two" (from PIE root *dwo- "two") + -plex, from PIE root *plek- "to plait." The noun in the sense of "house or other building so divided that it forms two dwelling places" (also sometimes "two-story apartment") is American English, by 1922.
late 14c., "easy to be bent, readily yielding to force or pressure without rupture," from Old French ploiable "flexible, bendable," from plier "to bend," from Latin plicare "to fold, lay" (from PIE root *plek- "to plait"). The figurative sense of "flexible in disposition, readily yielding to influence or argument" is by late 15c. Related: Pliably, pliability.
1680s, in anatomy, "an interlacing of nerves, vessels, or fibers," Modern Latin, literally "braid, network," noun use of past participle of Latin plectere "to twine, braid, fold," from suffixed form of PIE root *plek- "to plait." Original use in solar plexus "network of nerves in the abdomen" (see solar). General sense of "net-like arrangement of parts" is from 1760s. Related: Plexal.