CLAPPERBOARDS is validvalid

CLAPPERBOARD, a mechanical device to aid in synchronizing media tracks [n]

178,518 of 196,601 in NWL2023·also valid in CSW24

CLAPPERBOARD, a hinged board (or a set of hinged boards) clapped together in front of the camera before or after shooting a piece of film, to help synchronize sound and vision [n]