A taxi driver or the driver of a hack (a hired carriage or cab); an informal or slang term.
From hack (a taxi or carriage for hire, from hackney horses) + -ie (a diminutive or informal suffix). This informal English term became common in American English for cab drivers and has been used since at least the early 20th century.
The slang term 'hackie' for taxi driver is pure American and Australian English—British people say 'cabbie,' showing how the same basic profession got nicknamed differently on different sides of the Atlantic based on the word 'hack' vs. 'cab!'
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