next after the twenty-ninth; being the ordinal number for 30.
being one of 30 equal parts.


a thirtieth part, especially of one (1/30).
the thirtieth member of a series.

Origin of thirtieth

before 900; thirty + -eth2; replacing Middle English thrittythe, Old English thrītegtha Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019

Examples from the Web for thirtieth

Historical Examples of thirtieth

  • By the thirtieth time it has become a word like "snark" or "pobble."

    Alarms and Discursions

    G. K. Chesterton

  • She was one of those blondes who fade rapidly after their thirtieth year.


    Emile Zola

  • And now if ye will do battle, come again on the thirtieth day from hence.



  • "In the Thirtieth street station-house, sir," she briefly responded.

    The Masked Bridal

    Mrs. Georgie Sheldon

  • The Army of the Valley had its orders from Strasburg the night of the thirtieth.

    The Long Roll

    Mary Johnston

British Dictionary definitions for thirtieth



(usually prenominal)
  1. being the ordinal number of thirty in counting order, position, time, etc: often written 30th
  2. (as noun)the thirtieth of the month


  1. one of 30 approximately equal parts of something
  2. (as modifier)a thirtieth part
the fraction equal to one divided by 30 (1/30)
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 thirtieth

Middle English threttyth, from Old English þritigoða; see thirty + -th (1). Respelled 16c. to conform to new spelling of thirty.

Online Etymology Dictionary, © 2010 Douglas Harper