The name is a phono-semantic transliteration: 好 'good' + 市 'market' + 多 'many/much' — sounds roughly like 'Costco' while reading as 'good market with lots of stuff'. A textbook example of effective brand localization.
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好市多 is the official Taiwan name. In mainland China, Costco uses 开市客 (Kāishìkè) as its registered Chinese name.
