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Twi- is a combining form used like a prefix meaning “two” or “twice.” It appears in some older, mostly obsolete and rare terms.

Twi- ultimately comes from the Old English twi-, closely related to two, twelve, twice, twin, and even twig. The Latin counterpart to twi- is bi- and the Greek is di-.

Twi- isn’t productive in English today, with two, twin, and twice variously combined with words to do the former work of twi-. Combining forms derived from other languages, such as bi- or di-, are widely used, especially in technical terms.

One example of a common word that features twi- is twilight, “the soft, diffused light from the sky when the sun is below the horizon, either from daybreak to sunrise or, more commonly, from sunset to nightfall.” The word is first recorded in Middle English.

The word twilight combines twi-, meaning “two,” and light. But why this kind of light or period of day has a literal sense of “two or twice light” is uncertain. Some suppose it’s because twilight happens two times a day; others suggest that the twi- in the word has the sense of “half” (as if cut “in two”), alluding to the softer quality of this light.

What are some words that use the combining form twi-?

• twiarched
• twibill
• twiborn
• twifoil
• twiheaded
• twinature
• twitop

What are some other forms that twi- may be commonly confused with?

• thi-
• tri-

Not every word that begins with the exact letters twi- is necessarily using the combining forming twi- to denote “two,” such as twiddle, twirl, or twitch. Fiddle around with their history and meaning at our entries for the words.

A twibill is an archaic word for a kind of battle-ax, bill here being an old word meaning “sword.” How many blades does such an ax have?