factorialEnglishOxford Dictionary of Englishfactorial /fakˈtɔːriəl / ▸ noun Mathematics (Symbol: !) the product of a positive integer and all the integers below it; e.g. factorial four (4!) is equal to 24. ▪ the product of a series of factors in an arithmetical progression. ▸ adjective mainly Mathematics relating to a factor or factorial: a factorial design. – DERIVATIVES factorially adverb