E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Trivial,
strictly speaking, means “belonging to the beaten road.” (Latin, trivium, which is not tres viœ [three roads], but from the Greek tribo [to rub], meaning the worn or beaten path.) As what comes out of the road is common, so trivial means of little value. Trench connects this word with trivium (tres viœ or cross ways), and says the gossip carried on at these places gave rise to the present meaning of the word.
