"the property of being elastic," 1660s, from French élasticité, or else from elastic + -ity.
Entries linking to elasticity
elastic adj.
1650s, formerly also elastick, coined in French (1650s) as a scientific term to describe gases, "having the property of recovering its former volume after compression," from Modern Latin elasticus, from Greek elastos "ductile, flexible," related to elaunein "to strike, beat out," which is of uncertain origin; according to Watkins from an extended form of the PIE base *ele- "to go."
Applied to solids from 1670s, "having the power of returning to the form from which it is bent, etc., as soon as the applied force is removed." Figurative use by 1859. The noun meaning "piece of elastic material," originally a cord or string woven with rubber, is from 1847, American English.
-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]