1) a set of toothed wheels working together in a machine, e.g. to connect the engine of a vehicle with the road wheels (gear)

2) one of many kinds of tool with a toothed edge, used for cutting wood, metal; to cut (wood) with a saw; of see (saw)

3) a sound as of a bullet going through the air, or of the sudden tearing of cloth; a device with two toothed metal or plastic edges fastened together by means of a sliding tab, used for fastening articles of clothing; to open or close a coat, bag etc using a zip (zip)