practicability (n.)

1670s, "capable of being performed or affected," from French pratiquable (1590s), from pratiquer "to practice," from Medieval Latin practicare "to practice," from Late Latin practicus, ultimately from Greek (see practical). By 1710 as "capable of being actually used."

Possible notes that which may or might be performed if the necessary powers or means can or could be obtained ; practicable is limited to things which may he performed by the means that one possesses or can obtain. [Century Dictionary] 

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]