Each of two or more different physical forms in which an element can exist. Graphite, charcoal, and diamond are all allotropes of carbon.
- ‘Two allotropes of the element exist, accounting for the slight variation in densities.’
- ‘A third allotrope occurs as an amorphous brown powder with a density of 2.350 grams per cubic centimeter.’
- ‘Incredibly lightweight carbon nanofoams, essentially a fifth major allotrope of carbon, were discovered several years ago.’
- ‘Each of these allotropes of phosphorous also has its own subset of forms.’
- ‘Arsenic has two allotropes, yellow arsenic and metallic arsenic, which is brittle.’
Late 19th century: back-formation from allotropy.