Chemistry . 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; atomic weight: 58.71; atomic number: 28; specific gravity

8.9 at 20?C.

a cupronickel coin of the U.S., the 20th part of a dollar, equal to five cents.

a nickel coin of Canada, the 20th part of a dollar, equal to five cents.

to cover or coat with nickel; nickel-plate.

Slang . costing or worth five dollars

a nickel bag of heroin.