The Collaborative International Dictionary of English v.0.48:

Escheat \Es*cheat"\, n. [OE. eschete, escheyte, an escheat, fr.
   OF. escheit, escheoit, escheeite, esheoite, fr. escheoir (F.
   ['e]choir) to fall to, fall to the lot of; pref. es- (L. ex)
   + cheoir, F. choir, to fall, fr. L. cadere. See Chance, and
   cf. Cheat.]
   1. (Law)
      (a) (Feud. & Eng. Law) The falling back or reversion of
          lands, by some casualty or accident, to the lord of
          the fee, in consequence of the extinction of the blood
          of the tenant, which may happen by his dying without
          heirs, and formerly might happen by corruption of
          blood, that is, by reason of a felony or attainder.
          --Tomlins. --Blackstone.
      (b) (U. S. Law) The reverting of real property to the
          State, as original and ultimate proprietor, by reason
          of a failure of persons legally entitled to hold the
          same.
          [1913 Webster]

   Note: A distinction is carefully made, by English writers,
         between escheat to the lord of the fee and forfeiture
         to the crown. But in this country, where the State
         holds the place of chief lord of the fee, and is
         entitled to take alike escheat and by forfeiture, this
         distinction is not essential. --Tomlins. Kent.
      (c) A writ, now abolished, to recover escheats from the
          person in possession. --Blackstone.
          [1913 Webster]

   2. Lands which fall to the lord or the State by escheat.
      [1913 Webster]

   3. That which falls to one; a reversion or return
      [1913 Webster]

            To make me great by others' loss is bad escheat.
                                                  --Spenser.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Escheat \Es*cheat"\, v. i. [imp. & p. p. Esheated; p. pr. &
   vb. n. Escheating.] (Law)
   To revert, or become forfeited, to the lord, the crown, or
   the State, as lands by the failure of persons entitled to
   hold the same, or by forfeiture.
   [1913 Webster]

   Note: In this country it is the general rule that when the
         title to land fails by defect of heirs or devisees, it
         necessarily escheats to the State; but forfeiture of
         estate from crime is hardly known in this country, and
         corruption of blood is universally abolished. --Kent.
         Bouvier.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Escheat \Es*cheat"\, v. t. (Law)
   To forfeit. --Bp. Hall.
   [1913 Webster]

WordNet (r) 3.0 (2006):

escheat
    n 1: a reversion to the state (as the ultimate owner of
         property) in the absence of legal heirs
    2: the property that reverts to the state

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

ESCHEAT, title to lands. According to the English law, escheat denotes an
obstruction of the course of descent, and a consequent determination of the
tenure, by some unforeseen contingency; in which case the land naturally
results back, by a kind of reversion, to the original grantor, or lord of
the fee.. 2 Bl. Com. 244.
     2. All escheats, under the English law, are declared to be strictly
feudal, and to import the extinction of tenure. Wright on Ten. 115 to 117; 1
Wm. Bl. R. 123.
     3. But as the feudal tenures do not exist in this country, there are no
private persons who succeed to the inheritance by escheat. The state steps
in, in the place of the feudal lord, by virtue of its sovereignty, as the
original and ultimate proprietor of all the lands within its jurisdiction. 4
Kent, Com. 420. It seems to be the universal rule of civilized society, that
when the deceased owner has left no heirs, it should vest in the public, and
be at the disposal of the government. Code, 10, 10, 1; Domat, Droit Pub.
liv. 1, t. 6, s. 3, n. 1. Vide 10 Vin. Ab. 139; 1 Bro. Civ. Law, 250; 1
Swift's Dig. 156; 2 Tuck. Blacks. 244, 245, n.; 5 Binn. R. 375; 3 Dane's Ab.
140, sect. 24; Jones on Land Office Titles in Penna. 5, 6, 93. For the rules
of the Roman Civil Law, see Code Justinian, book 10.