-ity Definition

ətē, itē

suffix

State; quality.

Abnormality.

American Heritage

Used to form a noun from an adjective; especially, to form the noun referring to the state, property, or quality of conforming to the adjective's description.

Wiktionary

Used to form other nouns, especially abstract nouns.

Wiktionary

affix

State, character, or condition of being ____, or an instance of any of these.

Chastity, possibility.

Webster's New World

Origin of -ity

From French -ité, from Middle French -ité, from Old French -ete, -eteit (“-ity”), from Latin -itātem, from -itās, from Proto-Indo-European *-it- (suffix). Cognate with Gothic - (-iþa, “-th”), Old High German -ida (“-th”), Old English -þo, -þu, -þ (“-th”). More at -th.

From Wiktionary
ME -ite < OFr or L: OFr ité < L -itas < -i-, ending of stem, or thematic vowel + -tas, -ty

From Webster's New World College Dictionary, 5th Edition
Middle English -itie from Old French -ite from Latin -itās variant of -tās -ty

From American Heritage Dictionary of the English Language, 5th Edition