[ 'alətrəʊp ]
■ noun Chemistry each of two or more different physical forms in which an element can exist (e.g. graphite, charcoal, and diamond as forms of carbon).
Derivatives
allotropic adjective
allotropy ə'lɒtrəpi noun
Origin
C19: from Gk allotropos 'of another form', from allo- 'other' + tropos 'manner'.