thirty

noun

thir·​ty ˈthər-tē 

plural thirties

1

: a number equal to three times 10 see Table of Numbers

2

thirties plural : the numbers 30 to 39

specifically : the years 30 to 39 in a lifetime or century

3

: a sign of completion : end

—usually written 30

wrote thirty on the last page of the story

4

: the second point scored by a side in a game of tennis

thirtieth

ˈthər-tē-əth 

adjective or noun

thirty adjective

thirty pronoun, plural in construction

thirtyish

ˈthər-tē-ish 

adjective

Examples of thirty in a Sentence

The temperature outside is in the high thirties.

He is in his thirties.

Recent Examples on the Web

Photograph courtesy 2025 Adama Films / Shochiku Yasujirō Ozu, who made dozens of masterworks from the nineteen-thirties through the early sixties, is among the most misunderstood of great directors. —Dan Stahl, New Yorker, 1 May 2026

In the 1850s, all four writers were in their thirties or forties. —Literary Hub, 28 Apr. 2026

The curators Christine Riding and Lucy Bamford have brought together ten canvases that were originally shown in London between 1765 and 1773—the pieces thanks to which, during his mid-thirties, the North Midlands artist first secured a national reputation. —Julian Bell, The New York Review of Books, 25 Apr. 2026

Rectal cancer deaths are climbing among adults in their thirties and forties, at a rate that is accelerating much faster than deaths in this age group due to colon cancer, according to findings to be presented at the upcoming Digestive Disease Week conference. —Tom Gavin, EverydayHealth.com, 24 Apr. 2026

Word History

Etymology

Middle English thritty, from thritty, adjective, from Old English thrītig, from thrītig group of 30, from thrīe three + -tig group of ten; akin to Old English tīen ten

First Known Use

before the 12th century, in the meaning defined at sense 1

Phrases Containing thirty

• thirty-eight
• thirty-second note
• thirty-second rest
• thirty-thirty
• thirty-three
• thirty-two
• thirty-twomo

Rhymes for thirty

• birdie
• gurdy
• purdy
• sturdy
• wordy

Kids Definition

thirty

noun

thir·​ty ˈthərt-ē 

plural thirties

1

: a number equal to three times 10 see number

2

plural : the numbers 30 to 39

especially : the years 30 to 39 in a lifetime or century

thirtieth

-ē-əth 

noun or adjective

thirty adjective or pronoun