The prefix uni- means “one” or “single.” It comes from Latin and shows up in many English words to indicate that something has just one part, direction, or element.

A unicycle has one wheel, unlike a bicycle with two. A uniform is a single style of clothing worn by everyone in a group, making them look unified. When something moves in a unilateral direction, it goes one way. A unicorn is a mythical horse with a single horn on its forehead.

The prefix appears in more complex words too. When countries work together with a unified purpose, they act as one. Unison happens when voices or instruments play the same note at the same time, creating one sound instead of many. Something unique is one of a kind, existing alone without copies or matches.

When you spot uni- at the start of a word, you've found a clue about oneness or singularity, which helps unlock the word's meaning.