1590s, "quality of being trivial," from French trivialite or else from trivial + -ity. Meaning "a trivial thing or affair" is from 1610s. Related: Trivialities.
Entries linking to triviality
trivial adj.
"ordinary" (1580s); "insignificant, trifling" (1590s), from Latin trivialis "common, commonplace, vulgar," literally "of or belonging to the crossroads," from trivium "place where three roads meet," in transferred use, "an open place, a public place," from tri- "three" (see three) + via "road" (see via). The sense connection is "public," hence "common, commonplace."
The earliest use of the word in English was early 15c., a separate borrowing in the academic sense "of the trivium" (the first three liberal arts -- grammar, rhetoric, and logic); from Medieval Latin use of trivialis in the sense "of the first three liberal arts," from trivium, neuter of the Latin adjective trivius "of three roads, of the crossroads." Related: Trivially. For sense evolution to "pertaining to useless information," see trivia.
-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]