The Collaborative International Dictionary of English v.0.48:

Valentine \Val"en*tine\, n.
   1. A sweetheart chosen on St. Valentine's Day.
      [1913 Webster]

   2. A letter containing professions of love, or a missive of a
      sentimental, comic, or burlesque character, sent on St.
      Valentine's Day.
      [1913 Webster]

   St. Valentine's Day, a day sacred to St. Valentine; the
      14th of February. It was a very old notion, alluded to by
      Shakespeare, that on this day birds begin to mate. Hence,
      perhaps, arose the custom of sending love tokens at that
      time.
      [1913 Webster]

WordNet (r) 3.0 (2006):

valentine
    n 1: a sweetheart chosen to receive a greeting on Saint
         Valentine's Day; "will you be my valentine?"
    2: a card sent or given (as to a sweetheart) on Saint
       Valentine's Day

U.S. Gazetteer Places (2000):

Valentine, NE -- U.S. city in Nebraska
   Population (2000):    2820
   Housing Units (2000): 1373
   Land area (2000):     2.012706 sq. miles (5.212885 sq. km)
   Water area (2000):    0.002169 sq. miles (0.005617 sq. km)
   Total area (2000):    2.014875 sq. miles (5.218502 sq. km)
   FIPS code:            49950
   Located within:       Nebraska (NE), FIPS 31
   Location:             42.873686 N, 100.550308 W
   ZIP Codes (1990):     69201
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Valentine, NE
    Valentine


U.S. Gazetteer Places (2000):

Valentine, TX -- U.S. town in Texas
   Population (2000):    187
   Housing Units (2000): 138
   Land area (2000):     0.481008 sq. miles (1.245805 sq. km)
   Water area (2000):    0.000000 sq. miles (0.000000 sq. km)
   Total area (2000):    0.481008 sq. miles (1.245805 sq. km)
   FIPS code:            74648
   Located within:       Texas (TX), FIPS 48
   Location:             30.587504 N, 104.495498 W
   ZIP Codes (1990):     79854
   Note: some ZIP codes may be omitted esp. for suburbs.
   Headwords:
    Valentine, TX
    Valentine