# theta

> English word · Noun · IPA /ˈθiːtə/ · frequency rank #23,699

## Definitions
1. The eighth letter of the Modern Greek alphabet, ninth in Old Greek: Θ, θ.
2. The measure of an angle.
3. Pitch angle; the angle between an aircraft's longitudinal axis and the horizontal plane.
4. The sensitivity of the value of a derivative with respect to time; the "time decay".
5. Designating a level of brain activity as measured by electroencephalography having a frequency of between four and seven cycles per second (associated with drowsiness in adults).
6. The voiceless dental fricative represented by θ.

## Etymology
Borrowed from Ancient Greek θῆτα (thêta).

## Easily confused with
- **THT** (https://plainspell.com/en/vs/theta-vs-tht)
- **they** (https://plainspell.com/en/vs/theta-vs-they)
- **thot** (https://plainspell.com/en/vs/theta-vs-thot)
- **the** (https://plainspell.com/en/vs/the-vs-theta)
- **tea** (https://plainspell.com/en/vs/tea-vs-theta)
- **tha** (https://plainspell.com/en/vs/tha-vs-theta)
- **tet** (https://plainspell.com/en/vs/tet-vs-theta)
- **that** (https://plainspell.com/en/vs/that-vs-theta)
- **them** (https://plainspell.com/en/vs/them-vs-theta)
- **then** (https://plainspell.com/en/vs/then-vs-theta)
- **thee** (https://plainspell.com/en/vs/thee-vs-theta)
- **Theo** (https://plainspell.com/en/vs/theo-vs-theta)
- **tata** (https://plainspell.com/en/vs/tata-vs-theta)
- **Thea** (https://plainspell.com/en/vs/thea-vs-theta)
- **their** (https://plainspell.com/en/vs/their-vs-theta)
- **there** (https://plainspell.com/en/vs/there-vs-theta)
- **these** (https://plainspell.com/en/vs/these-vs-theta)
- **theme** (https://plainspell.com/en/vs/theme-vs-theta)
- **teeth** (https://plainspell.com/en/vs/teeth-vs-theta)
- **thats** (https://plainspell.com/en/vs/thats-vs-theta)

## Common misspellings (7)
`hteta`, `tehta`, `theat`, `thetta`, `thheta`, `thtea`, `ttheta`

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/theta