Meaning

noun the cardinal number that is the product of ten and three

adjective being ten more than twenty

originFrom 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. Cognate with Scots therty, tretty (“thirty”), West Frisian tritich (“thirty”), Dutch dertig (“thirty”), German dreißig (“thirty”).

Etymology from Wiktionary, CC BY-SA 3.0