—n. 1. Chem.a hard, silvery-white, ductile and malleable metallic element, allied to iron and cobalt, not readily oxidized: used chiefly in alloys, in electroplating, and as a catalyst in organic synthesis. Symbol: Ni; at. wt.: 58.71; at. no.: 28; sp. gr.: 8.9 at 20°C.
2. a cupronickel coin of the U.S., the 20th part of a dollar, equal to five cents.
3. a nickel coin of Canada, the 20th part of a dollar, equal to five cents.
—v.t. to cover or coat with nickel; nickel-plate.
—adj. Slang.costing or worth five dollars: a nickel bag of heroin.