二十

twenty / 20

twenty; 20

two / 2 / (Beijing dialect) stupid

ten / 10

blackjack (card game)

three sevens are twenty-one (idiom) / the facts of the matter / the actual situation

regardless of the consequences / recklessly relying on a hopelessly optimistic forecast

20th century

twenty four dynastic histories (or 25 or 26 in modern editions)

the twenty-eight constellations

26 years old

It's a long and intricate story, I hardly know where to start.

21st century

the Japanese Twenty-One Demands of 1915