WordReference Random House Unabridged Dictionary of American English © 2015fac•to•ri•al^{}
(fak tôr**′**ē əl, -tōr**′**-), n.
- Mathematics[Math.]the product of a given positive integer multiplied by all lesser positive integers: The quantity four factorial (4!) = 4 · 3 · 2 · 1 = 24.
*Symbol: n!,* where *n* is the given integer.

adj.
Mathematics[Math.]of or pertaining to factors or factorials.
of or pertaining to a factor or a factory.
**fac•to****′**ri•al•ly, adv.
Collins Concise English Dictionary © HarperCollins Publishers::

**factorial** /fækˈtɔːrɪəl/ n - the product of all the positive integers from one up to and including a given integer. Factorial zero is assigned the value of one:
*factorial four is 1 × 2 × 3 × 4*. Symbol: *n*!, where *n* is the given integer

adj - of or involving factorials or factors

**facˈtorially** adv
'**factorial**' also found in these entries: