mid-15c., "worthy to be remembered, not to be forgotten," from Latin memorabilis "that may be told; worthy of being remembered, remarkable," from memorare "to bring to mind," from memor "mindful of" (from PIE root *(s)mer- (1) "to remember"). Related: Memorably; memorableness.
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/memorability">Etymology of memorability by etymonline</a>
Harper, D. (n.d.). Etymology of memorability. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/memorability