A compound can be separated into the individual elements that it is comprised of and an element can separated as far as its individual atoms. An atom represents the smallest possible part of an element that still retains the properties of that element.
Definition of nickel. 1  1 : a silver-white hard malleable ductile metallic element capable of a high polish and resistant to corrosion that is used chiefly in alloys and as a catalyst â see element table. 2  2a (1) : the U.S. 5-cent piece regularly containing 25 percent nickel and 75 percent copper (2) : the Canadian 5-cent pieceb : five cents.
Silvery white, tough, and harder than iron, nickel is widely familiar because of its use in coinage but is more important either as the pure metal or in the form of alloys for its many domestic and industrial applications. Elemental nickel very sparingly occurs together with iron in terrestrial and meteoric deposits.