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

The structure is a bit tricksier, flipping between the present — which finds our two inevitable lovers estranged and in their early thirties — and a staggered series of flashbacks catching up to it. —Guy Lodge, Variety, 8 Jan. 2026

And with temperatures set to drop into the thirties that evening, quickly finding the missing woman became all the more important. —Outside, 6 Jan. 2026

Beginning in the nineteen-thirties, the archdiocese, led by Cardinal George Mundelein, had been allied with the Democratic Party and labor unions, and had promoted social activism through groups such as Young Christian Workers and the Catholic Interracial Council. —Paul Elie, New Yorker, 5 Jan. 2026

In her thirties she will get married, have kids and then focus on advancing in her career. —Lizz Schumer, PEOPLE, 4 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