To be inappropriate, unsuit, or unfitting for someone; to look bad on or not suit someone (archaic).
From dis- + become (from Old English becuman, 'to come to'). This archaic verb was used in early modern English when 'unbecoming' behavior was discussed.
Disbecome is pure Shakespeare-era English — it meant 'looks bad on you,' but we replaced it with 'unbecoming' and forgot the original verb entirely.
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