[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).