The Collaborative International Dictionary of English v.0.48:

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.
   [1913 Webster]

WordNet (r) 3.0 (2006):

peninsula
    n 1: a large mass of land projecting into a body of water

Moby Thesaurus II by Grady Ward, 1.0:

34 Moby Thesaurus words for "peninsula":
   Africa, Antarctica, Asia, Australia, Eurasia, Eurasian landmass,
   Europe, North America, South America, bill, breakwater, cape,
   chersonese, continent, coral reef, delta, foreland, head, headland,
   hook, landmass, main, mainland, mull, naze, ness, point,
   promontory, reef, sandspit, spit, spur, subcontinent, tongue



U.S. Gazetteer Places (2000):

Peninsula, OH -- U.S. village in Ohio
   Population (2000):    602
   Housing Units (2000): 254
   Land area (2000):     4.674119 sq. miles (12.105912 sq. km)
   Water area (2000):    0.010029 sq. miles (0.025976 sq. km)
   Total area (2000):    4.684148 sq. miles (12.131888 sq. km)
   FIPS code:            61574
   Located within:       Ohio (OH), FIPS 39
   Location:             41.240755 N, 81.556363 W
   ZIP Codes (1990):     44264
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Peninsula, OH
    Peninsula