An unfaceted gem.    From Wordnet, Princeton University. 

Noun : They carefully examined every facet of the argument.    From Dictionary.com. 

Thomas began initially for himself, working in copper and sterling silver with semi-precious cabochon (unfaceted) stones, broadening his oeuvre into gold and precious gems.    From Wordnik.com.  [One-of-a-Kind Geoff Thomas Jewelry Designs] Reference

Aside from the eight-pointed cross in his lapel, the only ornamentation or jewelry he wore consisted of a small, exquisitely thin gold watch on his left wrist, and, on the ring finger of his left hand, a gold signet ring set with a single, flat, unfaceted diamond which was delicately engraved with the Tarnhorst coat of arms.    From Wordnik.com.  [Anchorite] Reference