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). Sporting sense "reserve of players" (in baseball, North American football, etc.) is by 1909, from literal sense of place 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.
1892, baseball slang; see bench.
The days for "bench-warmers" with salaries are also past. [New York Sporting News, Jan. 9, 1892]
Old English had bencsittend "one who sits on a bench."
"peripatetic quack; one who sells nostrums at fairs, etc.," in Johnson's words, "a doctor that mounts a bench in the market, and boasts his infallible remedies and cures;" 1570s, from Italian montambanco, contraction of monta in banco "quack, juggler," literally "mount on bench" (to be seen by crowd), from monta, imperative of montare "to mount" (see mount (v.)) + banco, variant of banca "bench," from a Germanic source (see bench (n.)). Figurative and extended senses, in reference to any impudent pretender or charlatan, are from 1580s. Related: Mountebankery.
There probably was an Old English cognate but it is not attested in surviving documents. The nasalized form likely is a variant of Old Norse bakki "(river) bank, ridge, mound; cloud bank," cognate with Swedish backe, Danish bakke "hill, rising ground."
