early 15c., "of or pertaining to history, conveying information from the past," with -al (1) + Latin historicus "of history, historical," from Greek historikos "historical; of or for inquiry," from historia (see history). For sense differentiation, see historic. Meaning "narrated or mentioned in history" (as opposed to what is fiction or legend) is from 1843. Related: Historically.
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]
<a href="https://www.etymonline.com/word/historicity">Etymology of historicity by etymonline</a>
Harper, D. (n.d.). Etymology of historicity. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/historicity