[they-tuh, thee-]


the eighth letter of the Greek alphabet (Θ, θ).
the consonant sound represented by this letter.

Origin of theta

1595–1605; < Greek thêta < Semitic See teth Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for theta

Contemporary Examples of theta

Historical Examples of theta

  • Under the signature of Theta, he has since been a regular contributor of verses to that journal.

  • A tree in a prairie on a celestial body, as far as Theta of Orion is from Capella, is perfectly visible to us.


    Camille Flammarion

  • Next to Aldebaran in the V is the interesting double star Theta, which we can see as two distinct stars without a telescope.

    Astronomy for Young Folks

    Isabel Martin Lewis

  • The Latin language, wanting both the sound of the Greek theta, and the sign to express it (θ) rendered it by th.

    The English Language

    Robert Gordon Latham

  • The Gothic alphabet, in fact, as used in this country, had a Theta for expressing in one letter our present t and h conjoined.

    The Book-Hunter

    John Hill Burton

British Dictionary definitions for theta



the eighth letter of the Greek alphabet (Θ, θ), a consonant, transliterated as th
the lower-case form of this letter used in phonetic transcription to represent the voiceless dental fricative th as in thick, bothCompare edh

Word Origin for theta

C17: from Greek, of Semitic origin; compare Hebrew tēth
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

Word Origin and History for theta

eighth letter of the Greek alphabet; in ancient Greece, written on ballots to indicate a vote for a sentence of "death" (thanatos), hence occasional allusive use for "death."

Online Etymology Dictionary, © 2010 Douglas Harper

theta in Medicine


[thātə, thē-]


The eighth letter of the Greek alphabet.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.