twenty-first
UK: ˈtwenti ˈfɜːst | US: ˈtwɛnti ˈfɜrst
adj. coming immediately after the twentieth in a sequence
n. the ordinal number corresponding to twenty-one in a series
The word combines "twenty," derived from Old English "twēntig" (a compound of "twēn" (two) + "-tig" (group of ten)), and "first," from Old English "fyrst" (foremost in position or time). The hyphenated form "twenty-first" follows the standard English pattern for ordinal numbers beyond "twentieth," preserving the original spelling of both components.
She celebrated her twenty-first birthday with a grand party.
The twenty-first chapter of the book reveals the climax.
This is the twenty-first time I’ve reminded you to clean your room.
The twenty-first century began on January 1, 2001.
He finished in twenty-first place in the marathon.