Source : Webster's Revised Unabridged Dictionary (1913)

Elder \El"der\, n. [OE. ellern, eller, AS. ellen, cf. LG.
   elloorn; perh. akin to OHG. holantar, holuntar, G. holunder;
   or perh. to E. alder, n.] (Bot.)
   A genus of shrubs ({Sambucus}) having broad umbels of white
   flowers, and small black or red berries.

   Note: The common North American species is {Sambucus
         Canadensis}; the common European species ({S. nigra})
         forms a small tree. The red-berried elder is {S.
         pubens}. The berries are diaphoretic and aperient.

   {Box elder}. See under 1st {Box}.

   {Dwarf elder}. See {Danewort}.

   {Elder tree}. (Bot.) Same as {Elder}. --Shak.

   {Marsh elder}, the cranberry tree {Viburnum Opulus}).

Box \Box\ (b[o^]ks), n. [As. box, L. buxus, fr. Gr. ?. See {Box}
   a case.] (Bot.)
   A tree or shrub, flourishing in different parts of the world.
   The common box ({Buxus sempervirens}) has two varieties, one
   of which, the dwarf box ({B. suffruticosa}), is much used for
   borders in gardens. The wood of the tree varieties, being
   very hard and smooth, is extensively used in the arts, as by
   turners, engravers, mathematical instrument makers, etc.

   {Box elder}, the ash-leaved maple ({Negundo aceroides}), of
      North America.

   {Box holly}, the butcher's broom ({Russus aculeatus}).

   {Box thorn}, a shrub ({Lycium barbarum}).

   {Box tree}, the tree variety of the common box.

Source : WordNet®

box elder
     n : common shade tree of eastern and central United States [syn:
          {ash-leaved maple}, {Acer negundo}]