The Collaborative International Dictionary of English v.0.48:

Merrythought \Mer"ry*thought`\, n.
   The forked bone of a fowl's breast; -- called also
   wishbone. See Furculum.
   [1913 Webster]

   Note: It is a sportive custom for two persons to break this
         bone by pulling the ends apart to see who will get the
         longer piece, the securing of which is regarded as a
         lucky omen, signifying that the person holding it will
         obtain the gratification of some secret wish.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Wishbone \Wish"bone`\, n.
   The forked bone in front of the breastbone in birds; --
   called also merrythought, and wishing bone. See
   Merrythought, and Furculum.
   [1913 Webster]

WordNet (r) 3.0 (2006):

wishbone
    n 1: the furcula of a domestic fowl [syn: wishbone, wishing
         bone]

Moby Thesaurus II by Grady Ward, 1.0:

45 Moby Thesaurus words for "wishbone":
   Tarnkappe, V, branch, breast, cap of darkness, chicken foot,
   crotch, crutch, dark meat, delta, drumstick, fan, fern seed, fork,
   furcula, furculum, giblets, groin, inguen, leg, magic belt,
   magic carpet, magic ring, magic spectacles, magic wand,
   merrythought, neck, offshoot, oyster, prong, ramification,
   seven-league boots, stem, thigh, trident, turkey foot, wand,
   white meat, wing, wish-bringer, wish-giver, wishing bone,
   wishing cap, wishing stone, wishing well