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

Narges, a general practitioner in her thirties, fashioned a tourniquet from a head scarf to save the woman’s leg from a bullet wound. —Cora Engelbrecht, New Yorker, 11 Feb. 2026

Laxness had been visiting her hotels in Rome since the thirties. —Literary Hub, 11 Feb. 2026

And for anyone who's gone from twenties to thirties and gone from no kids to kids. —Dalton Ross, Entertainment Weekly, 1 Feb. 2026

In the late 1950s, a psychoanalyst named Elliott Jaques was the first to argue that people in their mid-thirties, primarily men, could experience a yearslong bout of depression brought on by the realization of one’s own mortality. —Tristan Bove, Fortune, 29 Jan. 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