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.

---

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

---

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

Hermen Hulst and his co-CEO Hideaki Nishino spoke to the BBC as Sony celebrates the thirtieth anniversary of the console being launched.

From BBC • Dec. 3, 2024

All that we know is that he passed away in the intake room of the jail one day after his thirtieth birthday.

From Slate • Oct. 25, 2022

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

From Textbooks • May 6, 2020

Every fifth day was market day—not the seventh or thirtieth, nothing you could give a name like “Saturday,” or “The First of the Month,” but every thumb if you kept the days in your hand.

From "The Poisonwood Bible" by Barbara Kingsolver