Banister

google

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mid 17th century: from earlier barrister, alteration of baluster.

wiktionary

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Alteration of earlier barrester, ballester, corruptions of baluster.

etymonline

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banister (n.)

1660s, unexplained corruption of baluster (q.v.). As late as 1848 it was identified as a vulgar term, but it is now accepted. Another 17c. corrupted form is barrester. Surname Bannister is unrelated, from Old French banastre "basket," hence, "basket-maker."