c. 1600, "that which constitutes a cause," from causal + -ity. From 1640s as "the relation of cause to effect."
Entries linking to causality
causal adj.
1530s, in grammar and logic, "expressing a cause," from Latin causalis "relating to a cause," from causa "a cause, reason" (see cause (n.)). From 1560s as "relating to a cause or causes;" 1640s as "being a cause, producing effects."
-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]