From Longman Dictionary of Contemporary Englishhard-bittenˌhard-ˈbitten adjective EXPERIENCEDnot easily shocked or upset, because you have had a lot of experience a hard-bitten cop
Examples from the Corpus
hard-bitten• Miss Davies is not really the tough, hard-bitten businesswoman that she appears to be.• Jensen's experience in prison left him hard-bitten, cynical, and ruthless.• a hard-bitten detective• That was hard-bitten, hard-nosed, hard-drinking newshound Edgar Allan Poe.• The hard-bitten men round the table knew better than to make that mistake.• He said he adored hard-bitten policemen.• Very few teachers are irredeemable, however hard-bitten they may appear.• Not one of them's a hard-bitten tom, the kind you'd find on the streets. 