"capability of being molded or formed; property of giving form or shape to matter," 1768, from plastic (adj.) + -ity.
Entries linking to plasticity
plastic adj.
1630s, "capable of shaping or molding a mass of matter," from Latin plasticus, from Greek plastikos "fit for molding, capable of being molded into various forms; pertaining to molding," also in reference to the arts, from plastos "molded, formed," verbal adjective from plassein "to mold" (see plasma). Related: Plastically.
Hence "capable of change or of receiving a new direction" (1791). The surgical sense of "remedying a deficiency of structure" is recorded by 1839 (in plastic surgery). Meaning "made of plastic" is from 1909; this was picked up in counterculture slang and given an extended meaning "false, superficial" (1963). Plastic explosive (n.) "explosive material with a putty-like consistency" is attested from 1894.
-ity
word-forming element making abstract nouns from adjectives and meaning "condition or quality of being ______," from Middle English -ite, from Old French -ete (Modern French -ité) and directly from Latin -itatem (nominative -itas), suffix denoting state or condition, composed of -i- (from the stem or else a connective) + the common abstract suffix -tas (see -ty (2)).
Roughly, the word in -ity usually means the quality of being what the adjective describes, or concretely an instance of the quality, or collectively all the instances; & the word in -ism means the disposition, or collectively all those who feel it. [Fowler]