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 some ways, Curley sees these values reflected in the average age of attendees at ARC, skewing more toward fans in their thirties and older, whereas Lolla, North Coast and Summer Smash garner much younger crowds. — Jessi Roti, Chicago Tribune, 28 Aug. 2026

Smith-Stewart organized it with curator Caitlin Monachino after more than 100 studio visits across Connecticut, eventually choosing 40 artists ranging in age from their thirties to their eighties. — Daniel Cassady, ARTnews.com, 27 Aug. 2026

What worked in our thirties may no longer work in later life. — Nia Bowers, USA Today, 25 Aug. 2026

The terrorist would probably be in their twenties or thirties. — Rozina Ali, New Yorker, 21 Aug. 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