gensym

gensym /jen'sim/  [from MacLISP for `generated symbol']
   1. v.  To invent a new name for something temporary, in such a way
   that the name is almost certainly not in conflict with one already
   in use.  2. n.  The resulting name.  The canonical form of a gensym
   is `Gnnnn' where nnnn represents a number; any LISP hacker would
   recognize G0093 (for example) as a gensym.  3. A freshly generated
   data structure with a gensymmed name.  Gensymmed names are useful
   for storing or uniquely identifying crufties (see {cruft}).