twenty /ˈtwɛnti/number 1noun 4forms 2phrases 3 number1 •the number 20, which comes after 19 noun4 •[in the plural] The numbers twenty (20) to twenty-nine (29).She looks like she's in her early twenties, perhaps 21 or 22 years old? •(informal) A banknote with a denomination of 20.The waiter’s face lit up when I gave him a twenty. •10-20 (location).What’s your twenty, good buddy? •(UK, historical) An old English division of infantry. formstwenties · twenty-somethings Phrases with twenty twenty to the dozenvery fast, fluently twenty-twenty hindsightA perfect understanding of events only after they have happened. twenty winksA very short sleep.