"quality of being advisable or expedient," 1778 (in a letter from George Washington at Valley Forge), from advisable + -ity. Advisableness is from 1731.
Entries linking to advisability
advisable adj.
1640s, "prudent, expedient, proper to be advised," from advise (v.) + -able (q.v.). It also can mean "open to advice" (1660s), but this is rare.
-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]