EXCH

EXCH /eks'ch*/ or /eksch/ vt.  To exchange two things,
   each for the other; to swap places.  If you point to two people
   sitting down and say "Exch!", you are asking them to trade
   places.  EXCH, meaning EXCHange, was originally the name of a
   PDP-10 instruction that exchanged the contents of a register and a
   memory location.  Many newer hackers are probably thinking instead
   of the {{PostScript}} exchange operator (which is usually written
   in lowercase).