\Fac*to"ri*al\, a.
1. Of or pertaining to a factory. --Buchanan.
2. (Math.) Related to factorials.

\Fac*to"ri*al\, n. (Math.)
   (a) pl. A name given to the factors of a continued product
       when the former are derivable from one and the same
       function F(x) by successively imparting a constant
       increment or decrement h to the independent variable.
       Thus the product F(x).F(x + h).F(x + 2h) . . . F[x +
       (n-1)h] is called a factorial term, and its several
       factors take the name of factorials. --Brande & C.
   (b) The product of the consecutive numbers from unity up
       to any given number.