The Collaborative International Dictionary of English v.0.48:

Resin \Res"in\ (r[e^]z"[i^]n), n. [F. r['e]sine, L. resina; cf.
   Gr. "rhti`nh Cf. Rosin.]
   Any one of a class of yellowish brown solid inflammable
   substances, of vegetable origin, which are nonconductors of
   electricity, have a vitreous fracture, and are soluble in
   ether, alcohol, and essential oils, but not in water;
   specif., pine resin (see Rosin).
   [1913 Webster]

   Note: Resins exude from trees in combination with essential
         oils, gums, etc., and in a liquid or semiliquid state.
         They are composed of carbon, hydrogen, and oxygen, and
         they consist primarily of polymerized small molecules
         having carboxylic groups. Copal, mastic, guaiacum, and
         colophony or pine resin, are some of them. When mixed
         with gum, they form the gum resins, like asafetida and
         gamboge; mixed with essential oils, they form balsams,
         or oleoresins. They are also used in making varnishes.
         [1913 Webster]

   2. Any of various polymeric substance resembling the natural
      resins[1], prepared synthetically; -- they are used,
      especially in particulate form, in research and industry
      for their property of specifically absorbing or adsorbing
      substances of particular types; they are especially useful
      in separation processes such as chromatography; as, an
      ion-exchange resin.
      [PJC]

   Highgate resin (Min.), a fossil resin resembling copal,
      occuring in blue clay at Highgate, near London.

   Resin bush (Bot.), a low composite shrub (Euryops
      speciosissimus) of South Africa, having smooth pinnately
      parted leaves and abounding in resin.
      [1913 Webster]

WordNet (r) 3.0 (2006):

resin
    n 1: any of a class of solid or semisolid viscous substances
         obtained either as exudations from certain plants or
         prepared by polymerization of simple molecules [syn:
         resin, rosin]

Moby Thesaurus II by Grady Ward, 1.0:

75 Moby Thesaurus words for "resin":
   Canada balsam, Sonora lac, acacia, agar, amber, ambergris,
   ammoniac, amyrin, anime, balsam, bassorin, benjamin, benzoin,
   camphor, carob gum, carrageenin, chewing gum, chicle, colophony,
   copaiba, copal, copaline, dammar, elemi, euphorbium, frankincense,
   ghatti, guacin, guaiac, guaiacum, guar gum, gum, gum ammoniac,
   gum anime, gum arabic, gum archipin, gum benjamin, gum butea,
   gum copal, gum dammar, gum elemi, gum juniper, gum kauri, gum kino,
   gum labdanum, gum myrrh, gum opoponax, gum resin, gum rosin,
   gum sagapenum, gum sandarac, gum shellac, gum storax, gum-lac,
   gutta-percha, kino, labdanum, lac, lacquer, mastic, myrrh,
   oleoresin, olibanum, pitch, quince-seed gum, resinate, resinize,
   resins, rosin, sagapenum, sandarac, shellac, sterculia gum, storax,
   tragacanth