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).
[ concert + -ina ]