Eighteen - definition of eighteen by The Free Dictionary Define eighteen eighteen synonyms, eighteen pronunciation, eighteen translation, English dictionary definition of eighteen n 1 The cardinal number equal to 17 + 1 2 The 18th in a set or sequence eight·een′ adj pron American Heritage® Dictionary of the English Language,
18 (number) - Wikipedia 18 (eighteen) is the natural number following 17 and preceding 19 It is an even composite number 18 is a semiperfect number [1] and an abundant number In the classification of finite simple groups, there are 18 infinite families of groups [2]