device that enables something to be used in a way different from that for which it was intended or makes different pieces of apparatus compatible; adapter
Microsoft Computer Dictionary
n. A printed circuit board that enables a personal computer to use a peripheral device, such as a CD-ROM drive, modem, or joystick, for which it does not already have the necessary connections, ports, or circuit boards. Commonly, a single adapter card can have more than one adapter on it. Also called: interface card. See also controller, expansion board, network adapter, port1, video adapter.