The Collaborative International Dictionary of English v.0.48:

Mastic \Mas"tic\, n. [F., fr. L. mastiche, mastichum, Gr. ?, fr.
   ? to chew, because of its being used in the East for
   chewing.] [Written also mastich.]
   [1913 Webster]
   1. (Bot.) A low shrubby tree of the genus Pistacia
      (Pistacia Lentiscus), growing upon the islands and
      coasts of the Mediterranean, and producing a valuable
      resin; -- called also, mastic tree.
      [1913 Webster]

   2. A resin exuding from the mastic tree, and obtained by
      incision. The best is in yellowish white, semitransparent
      tears, of a faint smell, and is used as an astringent and
      an aromatic, also as an ingredient in varnishes.
      [1913 Webster]

   3. A kind of cement composed of burnt clay, litharge, and
      linseed oil, used for plastering walls, etc.
      [1913 Webster]

   Barbary mastic (Bot.), the Pistachia Atlantica.

   Peruvian mastic tree (Bot.), a small tree (Schinus Molle)
      with peppery red berries; -- called also pepper tree.

   West Indian mastic (Bot.), a lofty tree (Bursera
      gummifera) full of gum resin in every part.
      [1913 Webster]

WordNet (r) 3.0 (2006):

mastic tree
    n 1: an evergreen shrub of the Mediterranean region that is
         cultivated for its resin [syn: mastic, mastic tree,
         lentisk, Pistacia lentiscus]