cardioid

from WordNet (r) 3.0 (2006)

cardioid
    n 1: an epicycloid in which the rolling circle equals the fixed
         circle

from The Collaborative International Dictionary of English v.0.48

Cardioid \Car"di*oid\, n. [Gr. kardio-eidh`s heart-shaped;
   kardi`a heart + e'i^dos shape.] (Math.)
   An algebraic curve, so called from its resemblance to a
   heart.
   [1913 Webster]