• threety (obsolete or nonstandard); thirtie (obsolete)
• Arabic numerals: 30
• Roman numerals: XXX

From Middle English thirty, metathetic alternant of Middle English thriti, þrittiȝ, from Old English þrītiġ (“thirty”), from Proto-Germanic *þrīz tigiwiz (“thirty”, literally “three tens”), equivalent to three +‎ -ty.^[1][2] Cognate with Scots therty, tretty (“thirty”), West Frisian tritich (“thirty”), Dutch dertig (“thirty”), German dreißig (“thirty”).

• (Received Pronunciation) IPA^(key): /ˈθɜːti/

• Audio (UK):

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• (General American) enPR: thŭr′tē, IPA^(key): /ˈθɝti/, [ˈθɝɾi]^[1][2][3][4]

• Audio (US):

  (file)

• Rhymes: -ɜː(ɹ)ti

thirty

1. The cardinal number occurring after twenty-nine and before thirty-one, represented in Arabic numerals as 30.
   • For quotations using this term, see Citations:thirty.

• triacontad

• (ordinal: the last of 30): thirtieth, trigesimal
• (adjectival form): tricenary
• (around 30): thirtyish
• (containing 30 of something): trigesimal
• (a 30-year-old person): tricenarian, thirtysomething
• (every 30 years): tricennial, trigintennial
• (30-sided figure): triacontahedron, triacontagon
• (30-sided): triacontahedral

thirty (plural thirties)

1. (slang) A rack of thirty beers.