catholicity (n.)

mid-14c., "of the doctrines of the ancient Church" (before the East/West schism), literally "universally accepted," from French catholique, from Church Latin catholicus "universal, general," from Greek katholikos, from phrase kath' holou "on the whole, in general," from kata "about" + genitive of holos "whole" (from PIE root *sol- "whole, well-kept").

Medieval Latin catholicus was practically synonymous with Christianus and meant "constituting or conforming to the church, its faith and organization" (as opposed to local sects or heresies). With capital C-, it was applied by Protestants to the Church in Rome by c. 1554, after the Reformation began in England. The general sense of "embracing all, universal" in English is from 1550s. The meaning "not narrow-minded or bigoted" is from 1580s. The Latin word was rendered in Old English as eallgeleaflic.

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]