eighteenth - Wiktionary, the free dictionary Noun eighteenth (plural eighteenths) The person or thing in the eighteenth position One of eighteen equal parts of a whole (informal) A party to celebrate an eighteenth birthday
Eighteenth - definition of eighteenth by The Free Dictionary eighteenth (ˈeɪˈtiːnθ) adj (Mathematics) (usually prenominal) a coming after the seventeenth in numbering or counting order, position, time, etc; being the ordinal number of eighteen: often written 18th