Source : Webster's Revised Unabridged Dictionary (1913)

Buckeye \Buck"eye`\, n.
   1. (Bot.) A name given to several American trees and shrubs
      of the same genus ({[AE]sculus}) as the horse chestnut.

   {The Ohio buckeye}, or {Fetid buckeye}, is {[AE]sculus
      glabra}.

   {Red buckeye} is {[AE]. Pavia}.

   {Small buckeye} is {[AE]. paviflora}.

   {Sweet buckeye}, or {Yellow buckeye}, is {[AE]. flava}.

   2. A cant name for a native in Ohio. [U.S.]

   {Buckeye State}, Ohio; -- so called because buckeye trees
      abound there.

Source : WordNet®

sweet buckeye
     n : a tall and often cultivated buckeye of the central United
         States