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

Sitting opposite us, three American tourists in their thirties are having a conversation. —Francesco Pacifico, The Dial, 9 Dec. 2025

By the thirties, Lauscha produced ninety-five per cent of the Christmas ornaments sold in the United States. —Emilia Petrarca, New Yorker, 8 Dec. 2025

The ending, too, undercuts the sensation that Gruesome Playground Injuries could just keep going and going through the rest of Doug and Kayleen’s scrapes—as Brown also noted back in 2011, the play carries the odd implication that life ends in your thirties. —Jackson McHenry, Vulture, 23 Nov. 2025

Most Gazans who had come of age or graduated from university in 2006 when Israel’s blockade was imposed were in 2023 reaching the second half of their thirties without ever having had a job, despite their impressive educational achievements. —Literary Hub, 10 Nov. 2025

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