arity

from WordNet (r) 3.0 (2006)

arity
    n 1: the number of arguments that a function can take

from The Free On-line Dictionary of Computing (8 July 2008)

arity

   <programming> The number of {arguments} a {function} or
   {operator} takes.  In some languages functions may have
   variable arity which sometimes means their last or only
   argument is actually a list of arguments.

   (1997-07-21)