thirtieth

American  

[thur-tee-ith] / ˈθɜr ti ɪθ /

adjective

1. next after the twenty-ninth; being the ordinal number for 30.

2. being one of 30 equal parts.

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noun

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

2. the thirtieth member of a series.

ˈthirtieth British  

/ ˈθɜːtɪɪθ /

adjective

1. (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

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noun

1. 1. one of 30 approximately equal parts of something

   2. ( as modifier )

      a thirtieth part

2. the fraction equal to one divided by 30 ( 1/ 30 )

Etymology

Origin of thirtieth

before 900; thirty + -eth ²; replacing Middle English thrittythe, Old English thrītegtha

Example Sentences

The difference: Your guests won’t have to feign enthusiasm after the thirtieth photo of you “holding up” the Leaning Tower of Pisa.

From The Wall Street Journal • Dec. 4, 2025

After the thirtieth consecutive month without rain, the townsfolk of San Francisco de Conchos in the northern Mexican state of Chihuahua gather to plead for divine intervention.

From BBC • Jul. 13, 2025

Find the thirtieth term of a sequence where the first term is −14 and the common difference is five.

From Textbooks • May 6, 2020

The Pioneer noted that the boxers were starting to look “a little groggy” by the thirtieth round.

From Slate • Jun. 2, 2019

On the thirtieth of September she sat through school and learned nothing.

From "Go Set a Watchman: A Novel" by Harper Lee