°(musici) A musical instrument, like the various
accordions, that is a member of the
free-reed family of musical instruments, typically having buttons on both ends. Concertinas are distinguished from accordions (piano or button) by the direction of the button travel when pushed. On a concertina, the buttons travel in the same direction as the bellows; on an accordion, the buttons move at a right angle to the direction of bellows travel.
°Something resembling a concertina, such as a folded book or a bus door.
verb
°to become
compressed into a shape reminiscent of a concertina.