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

In early December, 1945, a man and a woman in their thirties stepped onto a bus in Tel Aviv. — Paul Bloom, New Yorker, 6 Nov. 2026

The proportion of adults in their twenties and thirties living at home has continued to rise in recent years, and shows no sign of letting up. — Emma Burleigh, Fortune, 6 Nov. 2026

The apartments Svetlana cleaned belonged to people in their thirties who didn’t seem to leave the house much—there was trash from Amazon and Uber Eats everywhere. — Olivia Kan-Sperling, Artforum, 1 Nov. 2026

The protagonist, Shukichi, is a rootless part-time worker in his thirties living at Japan’s western edge. — Naman Ramachandran, Variety, 1 Nov. 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