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

RapidCAD

    A specially packaged Intel 486DX and a dummy
   floating point unit (FPU) designed as pin-compatible
   replacements for an Intel 80386 processor and 80387 FPU.
   Since the DX variant has a working on-chip FPU, a dummy FPU
   package is supplied to go in the 387 FPU socket.

   (1995-05-10)