bandit n.

Old English bannan "to summon, command, proclaim," from Proto-Germanic *bannan "to speak publicly" (used in reference to various sorts of proclamations), "command; summon; outlaw, forbid" (source also of Old Frisian bonna "to order, command, proclaim," Old High German bannan "to command or forbid under threat of punishment," German bannen "banish, expel, curse"), apparently a Germanic specialization from a suffixed form of PIE root *bha- (2) "to speak, tell, say" (source also of Old Irish bann "law," Armenian ban "word").

From mid-12c. as "to curse, condemn, pronounce a curse upon;" from late 14c. as "to prohibit;" these senses likely are via the Old Norse cognate banna "to curse, prohibit," and probably in part from Old French banir "to summon, banish" (see banish), a borrowing from Germanic. The sense evolution in Germanic was from "speak" to "proclaim a threat" to (in Norse, German, etc.) "curse, anathematize."

The Germanic root, borrowed in Latin and French, has been productive: banal, bandit, contraband, etc. Related: Banned; banning. Banned in Boston dates from 1920s, in allusion to the excessive zeal and power of that city's Watch and Ward Society. Ban the bomb as a slogan of the nuclear disarmament movement is from 1955.

late 14c., banischen, "to condemn (someone) by proclamation or edict to leave the country, to outlaw by political or judicial authority," from banniss-, extended stem of Old French banir "announce, proclaim; levy; forbid; banish, proclaim an outlaw" (12c., Modern French bannir), from a Germanic source (perhaps Frankish *bannjan "to order or prohibit under penalty"), from Proto-Germanic *bannan (see ban (v.)). The French word might be by way of Medieval Latin bannire, also from Germanic (compare bandit). The general sense of "send or drive away, expel" is from c. 1400. Related: Banished; banishing.

To banish is, literally, to put out of a community or country by ban or civil interdict, and indicates a complete removal out of sight, perhaps to a distance. To exile is simply to cause to leave one's place or country, and is often used reflexively: it emphasizes the idea of leaving home, while banish emphasizes rather that of being forced by some authority to leave it .... [Century Dictionary]