The Collaborative International Dictionary of English v.0.48:

Rosin \Ros"in\, n. [A variant of resin.]
   The hard, amber-colored resin left after distilling off the
   volatile oil of turpentine; colophony.
   [1913 Webster]

   Rosin oil, an oil obtained from the resin of the pine tree,
      -- used by painters and for lubricating machinery, etc.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Rosin \Ros"in\, v. t.
   To rub with rosin, as musicians rub the bow of a violin.
   [1913 Webster]

         Or with the rosined bow torment the string. --Gay.
   [1913 Webster]

WordNet (r) 3.0 (2006):

rosin
    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]
    v 1: rub rosin onto; "rosin the violin bow"