Plural of cabby, referring to multiple taxi drivers or people who operate cabs.
From cabby (an informal term for a cab driver, related to cab) plus the plural '-ies' ending, showing how informal British English created a diminutive form and then pluralized it.
British slang turned 'cab driver' into the friendly 'cabby' and 'cabbies,' which is the same pattern that created 'doggy' from 'dog' and 'kiddie' from 'kid'—diminutive suffixes make occupations sound more approachable and human.
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