allotropy vs allotropism

allotropy and allotropism both are nouns.

Word	Noun	Adjective	Verb	Adverb
allotropy	Yes	No	No	No
allotropism	Yes	No	No	No

As nouns, allotropy and allotropism are synonyms defined as:

allotropy and allotropism: the phenomenon of an element existing in two or more physical forms

allotropy (noun)	allotropism (noun)
the phenomenon of an element existing in two or more physical forms	the phenomenon of an element existing in two or more physical forms