twenty-first
ordinal number uk/ˌtwen.tiˈfɜːst/ us/ˌtwen.t̬iˈfɝːst/
第21，第二十一
21st written as a word
the twenty-first century 二十一世纪
twenty-first
noun [ C ] UK uk/ˌtwen.tiˈfɜːst/ us/ˌtwen.t̬iˈfɝːst/ (also twenty-first birthday)
21岁生日（西方的成人年龄）
the day on which a person reaches the age of 21 and is traditionally said, in Western societies, to become an adult
It's Jamie's twenty-first next Friday. 下周五是杰米的21岁生日。
Her dad gave her a car for her twenty-first. 她21岁生日时她父亲送了一辆车给她。