mid-15c., "so as to exclude;" 1560s, "that excludes," from Medieval Latin exclusivus, from exclus-, past participle stem of excludere (see exclude). Of monopolies, rights, franchises, etc., from 1760s; of social circles, clubs, etc., "unwilling to admit outsiders," from 1822. Related: Exclusively; exclusiveness.
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 exclusivity. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/exclusivity