The Free On-line Dictionary of Computing (30 December 2018):

COWSEL

   COntrolled Working SpacE Language.  Burstall and Popplestone,
   U Edinburgh, 1964-66.  LISP-like semantics with FORTH-like
   stack, and reverse Polish syntax.  Forerunner of POP.
   EPU-R-12, U Edinburgh (Apr 1966).