twenty-first
[ twen-tee-furst, twuhn- ]
/ ˈtwɛn tiˈfɜrst, ˈtwʌn- /
adjective
next after the twentieth; being the ordinal number for 21.
being one of 21 equal parts.
noun
a twenty-first part, especially of one (1/21).
the twenty-first member of a series.