n. & v.
--n. a musical instrument held in the hands and stretched and squeezed like bellows, having reeds and a set of buttons at each end to control the valves.
--v.tr. & intr. (concertinas, concertinaed or concertina'd, concertinaing) compress or collapse in folds like those of a concertina (the car concertinaed into the bridge).
Etymology: concert + -ina