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.

Cuckoobud \Cuck"oo*bud"\ (k??k"??-b?d`), n. (Bot.)
   A species of {Ranunculus} ({R. bulbosus}); -- called also
   {butterflower}, {buttercup}, {kingcup}, {goldcup}. --Shak.