Source : Webster's Revised Unabridged Dictionary (1913)

Peninsula \Pen*in"su*la\, n. [L. peninsula or paeninsula; paene
   almost + insula an island. See {Isle}.]
   A portion of land nearly surrounded by water, and connected
   with a larger body by a neck, or isthmus.

Source : WordNet®

peninsula
     n : a large mass of land projecting into a body of water