1. English: occupational name for a maker and repairer of wooden vessels such as barrels, tubs, buckets, casks, and vats, from Middle English couper, cowper (apparently from Middle Dutch kuper, a derivative of kup ‘tub’, ‘container’, which was borrowed independently into English as coop). The prevalence of the surname, its cognates, and equivalents bears witness to the fact that this was one of the chief specialist trades in the Middle Ages throughout Europe. In America, the English name has absorbed some cases of like-sounding cognates and words with similar meaning in other European languages, for example Dutch Kuiper.
2. Jewish (Ashkenazic): Americanized form of Kupfer and Kupper (see Kuper).
3. Dutch: occupational name for a buyer or merchant, Middle Dutch coper. Source