backbencher n.

"being behind, away from the front, in a backward direction," Middle English, from back (n.) and back (adv.); it is often difficult to distinguish from these when the word is used in combinations. Formerly with comparative backer (c. 1400), also backermore. To be on the back burner in the figurative sense of "postponed" is by 1960, from the image of a cook keeping a pot there to simmer while at work on another concoction at the front of the stove.

Middle English bench, from Old English benc "long seat," especially one without a back, from Proto-Germanic *bankon(source also of Old Frisian bank "bench," Old Norse bekkr, Danish bænk, Middle Dutch banc, Old High German banch). The group is cognate with bank (n.2) "natural earthen incline beside a body of water," and perhaps the original notion is "man-made earthwork used as a seat."

Used from late 14c. of a merchant's table. From c. 1300 in reference to the seat where judges sat in court, hence, by metonymy, "judges collectively, office of a judge." Hence also bencher "senior member of an inn of court" (1580s). The sporting sense "reserve of players" (in baseball, North American football, etc.) is by 1909, from a literal sense in reference to where players sit when not in action (attested by 1889). A bench-warrant (1690s) is one issued by a judge, as opposed to one issued by an ordinary justice or magistrate.