Source : Webster's Revised Unabridged Dictionary (1913)

Mizzenmast \Miz"zen*mast\, n. (Naut.)
   The hindmost mast of a three-masted vessel, or of a
   yawl-rigged vessel.

Source : WordNet®

mizzenmast
     n : third mast from the bow in a vessel having three or more
         masts; the after and shorter mast of a yawl, ketch, or
         dandy [syn: {mizenmast}, {mizzen}, {mizen}]