The Collaborative International Dictionary of English v.0.48:

Locket \Lock"et\, n. [F. loquet latch, dim. of OF. loc latch,
   lock; of German origin. See Lock a fastening.]
   [1913 Webster]
   1. A small lock; a catch or spring to fasten a necklace or
      other ornament.
      [1913 Webster]

   2. A little case for holding a miniature picture or lock of
      hair, usually suspended from a necklace or watch chain.
      [1913 Webster]

WordNet (r) 3.0 (2006):

locket
    n 1: a small ornamental case; usually contains a picture or a
         lock of hair and is worn on a necklace

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "locket":
   anklet, armlet, bangle, beads, bijou, bracelet, breastpin, brooch,
   chain, chaplet, charm, chatelaine, circle, coronet, crown, diadem,
   earring, fob, gem, jewel, necklace, nose ring, pin, precious stone,
   rhinestone, ring, stickpin, stone, tiara, torque, wampum,
   wristband, wristlet