They settled down in their thirties. The temperature fell into the thirties.
- the numbers or years, as of a century, from thirty through thirty-nine
Other Word Forms
Idioms and Phrasal Verbs
Origin of thirty
- Middle English thritty, thirty from Old English thrītig trei- in Indo-European roots
From American Heritage Dictionary of the English Language, 5th Edition
- From Middle English thirty, metathetic alternant of Middle English thritti, þrittiȝ, from Old English þritiÄ¡ (“thirty"), from Proto-Germanic *þrÄ«z tigiwiz (“thrity", literally “three tens"), equivalent to three +"Ž -ty. Cognate with Scots therty, tretty (“thirty"), West Frisian tritich (“thrity"), Dutch dertig (“thrity"), German dreißig (“thirty").