c. 1600, "unable to be heard," from Late Latin inaudibilis "inaudible," from in- "not" (see in- (1)) + audibilis (see audible). Used in Middle English in the sense "unfit to be heard" (mid-15c.). Related: Inaudibly. Classical Latin had inauditus "unheard, unheard of."
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]
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Harper, D. (n.d.). Etymology of inaudibility. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/inaudibility