Source : Webster's Revised Unabridged Dictionary (1913)

Sealing wax \Seal"ing wax`\
   A compound of the resinous materials, pigments, etc., used as
   a material for seals, as for letters, documents, etc.

Source : WordNet®

sealing wax
     n : fastener consisting of a resinous composition that is
         plastic when warm; used for sealing documents and parcels
         and letters [syn: {seal}]