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The Collaborative International Dictionary of English v.0.48 (gcide)

Allotropism \Al*lot"ro*pism\, Allotropy \Al*lot"ro*py\, n. [Gr.
? other direction, way, ? to turn: cf. F. allotropie.]
(Chem.)
The property of existing in two or more conditions which are
distinct in their physical or chemical relations.
[1913 Webster]

Note: Thus, carbon occurs crystallized in octahedrons and
other related forms, in a state of extreme hardness, in
the diamond; it occurs in hexagonal forms, and of
little hardness, in black lead; and again occurs in a
third form, with entire softness, in lampblack and
charcoal. In some cases, one of these is peculiarly an
active state, and the other a passive one. Thus, ozone
is an active state of oxygen, and is distinct from
ordinary oxygen, which is the element in its passive
state.
[1913 Webster]