Source : Webster's Revised Unabridged Dictionary (1913)

Buttercup \But"ter*cup`\, n. (Bot.)
   A plant of the genus {Ranunculus}, or crowfoot, particularly
   {R. bulbosus}, with bright yellow flowers; -- called also
   {butterflower}, {golden cup}, and {kingcup}. It is the
   {cuckoobud} of Shakespeare.

Source : WordNet®

buttercup
     n : any of various plants of the genus Ranunculus [syn: {butterflower},
          {butter-flower}, {crowfoot}, {goldcup}, {kingcup}]