tri

tri- is one of the most transparent roots in English: it simply means "three." It comes from both Latin trēs and Greek treis (and behind them the Proto-Indo-European *trei-), so it sits in front of words from both classical sources. Whenever you see tri- at the start of a word, your first guess should be "something to do with three," and you will be right far more often than not.

The family is wonderfully literal. A triangle has three angles. A tripod has three feet (Greek pod-, foot). A trio is a group of three, or a piece of music for three players. Triple, triplet, triplicate, trident (three teeth), triathlon (three sports), tricycle (three wheels) — the pattern almost never lies. This is the kind of root that pays off instantly, because the "three" is rarely hidden under a metaphor.

But there is one famous, delightful exception: trivial. To a Roman, a trivium was a place where three roads met (tri- + via, road) — a busy intersection where townsfolk bumped into each other and traded gossip and small talk. The chatter you picked up at the three-way crossroads was ordinary, everyday, of no real importance. So trivium's adjective, trivial, drifted away from "three roads" and came to mean "petty, unimportant." Its plural trivia became the English word for scraps of minor knowledge — hence the trivia quiz. (Later, medieval scholars also used trivium for the three basic subjects of study — grammar, logic, rhetoric — the foundation before the quadrivium of four.)

So the tri- family has two flavors: the huge, obedient group where three means exactly three, and the lone wanderer trivial, where three roads led the meaning somewhere nobody driving through would expect. Knowing the crossroads story turns the strangest member of the family into the most memorable one.