Source : Webster's Revised Unabridged Dictionary (1913)

Formalin \For"ma*lin\, n. [Formic + aldehyde + -in.] (Chem.)
   An aqueous solution of formaldehyde, used as a preservative
   in museums and as a disinfectant.

Source : WordNet®

formalin
     n : a 10% solution of formaldehyde in water; used as a
         disinfectant or to preserve biological specimens [syn: {formol}]