theta

theta — noun

1. Θ (uppercase) and θ (lowercase) are the capital and small forms of the eighth ch

1.nounB1
Definition

Θ (uppercase) and θ (lowercase) are the capital and small forms of the eighth character in the Greek writing system. This letter is widely used as a symbol in mathematics and science — for example, to label an unknown angle in geometry or to represent temperature in physics.

Example

Mathieu learned that the Greek letter θ stands for an unknown angle in geometry.

symbol for an angle in geometry

In physics class, Naoko used theta to mark the temperature in her formula.

used for temperature in physics

Common collocations
  • theta angle
  • theta value
  • theta function
  • letter theta
  • symbol theta

Grammar Patterns

theta + verb (singular)

Usage Note

Pronounced /ˈθiːtə/ (THEE-tuh) in both American and British English. The 'th' sound at the start does not exist in Mandarin or many other Asian languages, so learners often need extra practice saying it. In mathematics, θ is routinely used to label an unknown angle in trigonometry and geometry. In physics, lowercase θ often stands for temperature or an angle, while uppercase Θ may represent a thermodynamic quantity.

Common Mistakes

I wrote a small tita on my paper.
I wrote a small theta on my paper.
The letter is spelled theta, with 'th' and not 't'; the 'th' makes a soft sound like in 'think'.

Common collocations

Nouns

  • theta symbol
  • theta value
  • theta angle

Phrases

  • represented by theta
  • denoted by theta

Etymology

PhoenicianGreekLatinEnglish

Theta comes from the Greek word θῆτα (thēta), which the ancient Greeks adopted from the Phoenician letter teth. The sound it represented changed over time — in Classical Greek it was an aspirated 't' sound (/tʰ/), but in Modern Greek it is pronounced like the 'th' in 'thin' (/θ/). English borrowed the letter name through Latin, and it has been used in Western mathematics and science since the Renaissance.