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.

thirtieth 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

It’s hard to overlook, for instance, that this movie arrives in theatres in the same year as the thirtieth anniversary of Spike Lee’s “Do The Right Thing.”

From The New Yorker • Nov. 27, 2019

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

From Slate • Jun. 2, 2019

On that thirtieth day, Grace had huddled in bed and watched the clock tick down.

From "Far from the Tree" by Robin Benway