From Longman Dictionary of Contemporary Englishhalf-arsedhalf-arsed /ˌhɑːf ˈɑːst◂ $ ˈhæf ɑːrst/ British English, half-assed /ˌhɑːf ˈæst $ ˈhæf æst/ American English adjective [only before noun] informal 1 WORK HARDdoing something without making much effort He made a half-arsed attempt to clean up after the party.2 STUPID/NOT SENSIBLEcompletely stupid What a half-assed idea!
Examples from the Corpus
half-arsed• What half-arsed plot was that berk hatching now?• L7 aren't half-arsed rockers, they trample over most of their rivals, they don't want to be blokes. 