trivialyoudaoicibaDictYouDict[trivial 词源字典]
trivial: [15] Medieval educationists recognized seven liberal arts: the lower three, grammar, logic, and rhetoric, were known as the trivium, and the upper four, arithmetic, astronomy, geometry, and music, were known as the quadrivium. The notion of ‘less important subjects’ led in the 16th century to the use of the derived adjective trivial for ‘commonplace, of little importance’. Latin trivium itself was a compound noun formed from the prefix tri- ‘three’ and via ‘way, road’, and originally meant ‘place where three roads meet’.
=> three, via[trivial etymology, trivial origin, 英语词源]
trivial (adj.)youdaoicibaDictYouDict
"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.