masculinity (n.)

mid-14c., "belonging to the male grammatical gender;" late 14c., "of men, of male sex," from Old French masculin "of the male sex" (12c.), from Latin masculinus "male, of masculine gender," from masculus "male, masculine; worthy of a man," diminutive of mas (genitive maris) "male person, male," a word of unknown origin. The diminutive form might be by pairing association with femininus (see feminine). Meaning "having the appropriate qualities of the male sex, physically or mentally: Manly, virile, powerful" is attested by 1620s. As a noun, "masculine gender," from c. 1500.

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]