malleability (n.)

late 14c., "capable of being shaped or extended by hammering or rolling," from Old French malleable and directly from Medieval Latin malleabilis, from malleare "to beat with a hammer," from Latin malleus "hammer" (from PIE root *mele- "to crush, grind"). Figurative sense, of persons, "capable of being adapted by outside influence" is recorded from 1610s.

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]