promiscuity n.

c. 1600, of people or things, "mingled confusedly or indiscriminately, consisting of parts or individuals grouped together without order, consisting of a disorderly mix," from Latin promiscuus "mixed, indiscriminate, in common, without distinction, to which all are admitted without distinction," from pro (see pro-) + miscere "to mix" (from PIE root *meik- "to mix").

Meaning "indiscriminate in sexual relations" is recorded by 1857, from promiscuity in the related sense, the meaning then shading into "not restricted to one individual." The Latin adjective also was used sexually, with conubia (of sexual union between patricians and plebeians). Related: Promiscuously; promiscuousness.

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]