1. working badly or unreliably because of imperfections: "a car with faulty brakes"Similarmalfunctioningbrokendamageddefectivenot workingnot functioningin disrepairout of orderout of commissioninoperativeunsoundunusableuselessinformal:on the blinkon its last legskaputbustbustedconked outacting/playing upgone haywiregone phutdone forwonkydudknackeredduffon the fritzOppositeworkingfunctioning