Parallelogram, two of my dictionaries indicate that 'compass' is fine. The  Collins definition for  compass is 'an instrument used for drawing circles, measuring distances etc.'  The definition is prefaced with 'sometimes plural'  - which seems to indicate it doesn't have to be. The information in the ODE is very similar.  This  definition doesn't appear in Chambers, but the Times  puzzles aren't limited to any single dictionary.