A female shop assistant or saleswoman who works behind a counter, serving customers.
From 'counter' (the serving surface in a shop) plus 'maid' (from Old English 'mægden', a young woman or servant). This term parallels 'shopgirl' and was common before modern retail terminology.
Before 'sales associate' and 'cashier,' countermaid was the standard term for women working retail—now mostly found in historical fiction and vintage shop signs. Language changes as society and work changes!
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