Twenty thousand years ago, long before the invention of agriculture, humans lived a hunting and gathering way of life in small bands. Cooperation and social harmony were critical for the group to survive. In order to maintain this harmony, individuals who were disruptive to the group were banished.
Ban and Banish:
The etymology of the words ban and banish can be traced back to the Proto-Indo-European base *bha- which is also the base of the English words fame and phase. Out of the Indo-European *bha- came the Proto-Germanic *bannan, meaning “proclaim, command, forbid, which became bannan in Old English.
The modern sense of ban meaning “to prohibit” came into English in the late fourteenth century and seems to be related to the Old Norse cognate banna meaning “to curse, prohibit.” In other words, the Vikings (Norse) who had settled in England influenced the language.
The Proto-Indo-European base *bha- eventually became the Old French banir meaning "announce, proclaim; levy; forbid; banish, proclaim an outlaw." The Old French banir seems to have come from or been influenced by a Germanic source (some etymologists have suggested the Frankish *bannjan meaning "to order or prohibit under penalty"), or from the Vulgar Latin cognate *bannire. The English word banish emerged from the Old French in the fourteenth century.
What we see in looking at the etymology of ban and banish is that word evolution is often not a lineal evolution, but can be a bit convoluted.
Shun:
The word shun has its origins in the Old English scunian meaning “to avoid; abhor; desist; abstain; seek safety by concealment.” Linguists are uncertain about its origins prior to Old English. There are some who feel that it may have come from the Proto-Indo-European root *skeu- which meant “to cover, to hide.”
In American English, the term “shun-pike” emerged about 1911 to refer to a road that had been constructed to avoid tolls.
Ostracize:
Sometime in the 1640s, English incorporated the word ostracize with the meaning of “to exclude from society.” The word comes from the Greek ostrakizein meaning "to banish," literally "to banish by voting with potshards." John Ayto, in his Dictionary of Word Origins, explains:
“In ancient Greece, when it was proposed that a particular person should be sent into exile for a period, because he was becoming a danger to the state, a democratic vote was taken on the matter. The method of registering one’s vote was to inscribe the name of the prospective banishee on a piece of broken pottery. The pieces were counted, and if enough votes were cast against him away he would go for ten years.”
The way this is linguistically related to the later ostracise is that the fragment of pottery was called óstrakon in Greek.
Exile:
The word exile came into English about 1300 from the Old French essillier meaning "to exile, banish, expel, drive off". The source of the Old French essillier is the Late Latin exilare/exsilare, which is from the Latin exilium/exsilium meaning "banishment, exile; place of exile."
In Latin, exule meant a “banished person” and was formed with the prefix ex- meaning “out” and the Proto-Indo-European base *ul- meaning “go.” In Old French, this became the noun essil.
Note:
In etymologies, the * indicates that the Proto-Indo-European or prehistoric word has been reconstructed by historical linguists.