WordNet (r) 3.0 (2006):

treasure trove
    n 1: treasure of unknown ownership found hidden (usually in the
         earth) [syn: treasure trove, trove]
    2: any collection of valuables that is discovered; "her book was
       a treasure trove of new ideas"; "mother's attic was a
       treasure trove when we were looking for antiques"

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "treasure trove":
   bonus, bringing to light, buried treasure, casual discovery,
   catching, chance discovery, detection, determination, determining,
   disclosure, discovery, distinguishment, espial, excavation,
   exhumation, exposure, find, finding, finding out, foundling, gravy,
   invention, locating, location, lucky strike, recognition,
   rediscovery, revelation, serendipity, spotting, strike, trouvaille,
   trove, uncovering, unearthing, waifs, waifs and strays, windfall,
   windfall money, windfall profit



Bouvier's Law Dictionary, Revised 6th Ed (1856):

TREASURE TROVE. Found treasure.
     2. This name is given to such money or coin, gold, silver, plate, or
bullion, which having been hidden or concealed in the earth or other private
place, so long that its owner is unknown, has been discovered by accident.
Should the owner be found it must be restored to him; and in case of not
finding him, the property, according to the English law, belongs to the
king. In the latter case, by the civil law, when the treasure was found by
the owner of the soil, he was considered as entitled to it by the double
title of owner and finder; when found on another's property, one-half
belonged to the owner of the estate, and the other to the finder; when found
on public property, it belonged one-half to the public treasury, and the
other to the finder. Lecons du Dr. Rom. Sec. 350-352. This includes not only
gold and silver, but whatever may constitute riches, as vases, urns,
statues, &c.
     3. The Roman definition includes the same things under the word
pecunia; but the thing found must have a commercial value for ancient tombs
would not be considered a treasure. The thing must have been hidden or
concealed in the earth; and no one must be able to establish his right to
it. It must be found, by a pure accident, and not in consequence of search.
Dall. Dict. Propriete, art. 3, s. 3.
     4. According to the French law, le tresor est toute chose cachee ou
enfouie, sur laquelle personne ne peut justifier sa propriete, et qui est
decouverte par lo pur effet du hasard. Code Civ. 716. Vide 4 Toull. n. 34.
Vide, generally, 20 Vin. Abr. 414; 7 Com. Dig. 649; 1 Bro. Civ. Law, 237; 1
Blackstone's Comm. 295; Poth. Traite du Dr. de Propreite, art. 4.