Source : Webster's Revised Unabridged Dictionary (1913)

Cycloidal \Cy*cloid"al\ (-al), a.
   Pertaining to, or resembling, a cycloid; as, the cycloidal
   space is the space contained between a cycloid and its base.

   {Cycloidal engine}. See {Geometric lathe}.

Source : WordNet®

cycloidal
     adj : resembling a circle [syn: {cycloid}]