Source : Webster's Revised Unabridged Dictionary (1913)

Buttonwood \But"ton*wood`\, n. (Bot.)
   The {Platanus occidentalis}, or American plane tree, a large
   tree, producing rough balls, from which it is named; --
   called also {buttonball tree}, and, in some parts of the
   United States, {sycamore}. The California buttonwood is {P.
   racemosa}.

Source : WordNet®

buttonwood
     n : very large spreading plane tree of eastern and central North
         America to Mexico [syn: {American sycamore}, {American
         plane}, {Platanus occidentalis}]