tri

Tri is a combining form and a term used in many disciplines to indicate the number three. The prefix tri- comes from Latin tres, meaning three, and it appears in a wide range of words and concepts.

In everyday language, tri- forms many familiar terms such as triangle (a three-sided figure), tricycle (three wheels), tricolor (three colors), tripod (three legs), trimester (a period of three months), trilateral (involving three sides or parties), and triple (threefold). It also appears in chemical nomenclature for compounds with three identical or related groups, such as triglyceride (three fatty acid chains) or trimethyl (three methyl groups).

In science and mathematics, tri- denotes a triple arrangement or a three-part system. Examples include trimer (a molecule made of three subunits), triatomic (consisting of three atoms), and trigonometry (the study of triangles). In physics and engineering, tri-state logic describes circuits that can assume three possible states, such as true, false, and high impedance.

In music, a triad is a three-note chord that forms the harmonic basis of much Western harmony. The term tritone refers to an interval spanning three whole tones, historically described as dissonant and unstable.

In sports and culture, triathlon is a multi-discipline event combining three activities, typically swimming, cycling, and running. The root tri- also appears in numerous other compound terms across fields, preserving the general sense of “threefold” or “three-part.”

Overall, tri serves as one of the most productive prefixes in English, providing a concise way to express three-component structures, proportions, or concepts across many domains.