1) Chemical element 2) Element 
allotropy; allotropic; allotropism. Compare with isotope and polymorph. Some elements occur in several distinct forms called allotropes. Allotropes have different chemical and physical properties. For example, graphite and diamond are allotropes of carbon.
<chemistry> Any individual structural form of an element which comes in at least two different structural types. ... (09 Oct 1997) ... 
Element with more than one natural form
Type: Term Pronunciation: al′ō-trōp Definitions: 1. One of several forms, differing in physical properties, that an element may assume; carbon black, graphite, and diamonds are all allotropes of pure carbon.
Element with more than one natural form.
[n] - a structurally different form of an element
allotrope A substance that exists and is metastable in two or more physical forms over a given temperature range. Allotropes have different chemical and physical properties; for example, graphite and diamond are allotropes of carbon.
noun a structurally different form of an element; `graphite and diamond are allotropes of carbon`
An element which exist in two or more different forms in the same physical state. Diamond and Graphite are both allotropes of carbon yet diamond is hard and graphite is soft. Diamonds crystallize in the cubic crystal system, and Graphite crystallizes in the hexagonal system.
one of two or more existing forms of an element: Graphite and diamond are allotropes of carbon.