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]