/ ˈkʌnstəbl; NAmE ˈkɑːn-/ noun
(used especially when talking to a police officer of the lowest rank) = police constable :
Have you finished your report, Constable?
—see also chief constable
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WORD ORIGIN
Middle English originally the governor of a royal castle: from Old French conestable , from late Latin comes stabuli count (head officer) of the stable. The current sense dates from the mid 19th cent.