1610s, "state of being kindred; affinity of character or interests;" as if from Latin but apparently a modern formation; compare congenial + -ity.
Entries linking to congeniality
congenial adj.
1620s, "kindred, partaking of the same nature or natural characteristics," from assimilated form of Latin com "with, together" (see con-) + genialis "of birth," thus, "kindred" (from PIE root *gene- "give birth, beget," with derivatives referring to procreation and familial and tribal groups). Sense of "agreeable" is first recorded 1711 on the notion of "having natural affinity." Also compare congenital.
-ity
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]