natality n.

late 14c., "of or pertaining to birthdays;" mid-15c., "of or pertaining to one's birth," from Latin natalis "pertaining to birth or origin," from natus, past participle of nasci "to be born" (Old Latin gnasci), from PIE root *gene- "give birth, beget." It is the learned form of Noel, which was the French vernacular word.

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]