1. [n]  any of a class of solid or semisolid viscous substances obtained either as exudations from certain plants or prepared by polymerization of simple molecules
2. [v]  rub rosin onto, as of violin bows

ROSIN is a 5 letter word that starts with R.

1. \Ros"in\, n. [A variant of resin.]
   The hard, amber-colored resin left after distilling off the
   volatile oil of turpentine; colophony.
   
   {Rosin oil}, an oil obtained from the resin of the pine tree,
      -- used by painters and for lubricating machinery, etc.
   
   

2. \Ros"in\, v. t.
   To rub with rosin, as musicians rub the bow of a violin.
   
         Or with the rosined bow torment the string. --Gay.
   
   

found only in Authorized Version, margin, Ezek. 27:17, Heb. tsori, uniformly rendered elsewhere "balm" (q.v.), as here in the text. The Vulgate has resinam, rendered "rosin" in the Douay Version. As used, however, by Jerome, the Lat. resina denotes some odoriferous gum or oil.