Source : Webster's Revised Unabridged Dictionary (1913)

Urethane \U*reth"ane\, n. [F. ur['e]thane. See {Urea}; {Ether}.]
   (Org. Chem.)
   A white crystalline substance, {NH2.COOC2H5}, produced by the
   action of ammonia on ethyl carbonate or by heating urea
   nitrate and ethyl alcohol. It is used as a hypnotic,
   antipyretic, and antispasmodic. Hence, any ester of carbamic
   acid.

Urethane \U*reth"ane\, n. (Chem.)
   A white crystalline substance, {NH2.CO.OC2H5}, produced by
   the action of ammonia on ethyl carbonate. It is used somewhat
   in medicine as a hypnotic. By extension, any one of the
   series of related substances of which urethane proper is the
   type.

Source : WordNet®

urethane
     n : an ester of carbamic acid