The Collaborative International Dictionary of English v.0.48:

Usufruct \U"su*fruct\ (?; 277), n. [L. usufructus, ususfructus,
   usus et fructus; usus use + fructus fruit.] (Law)
   The right of using and enjoying the profits of an estate or
   other thing belonging to another, without impairing the
   substance. --Burrill.
   [1913 Webster]

WordNet (r) 3.0 (2006):

usufruct
    n 1: a legal right to use and derive profit from property
         belonging to someone else provided that the property itself
         is not injured in any way

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

USUFRUCT, civil law. The right of enjoying a thing, the property of which is
vested in another, and to draw from the same all the profit, utility and
advantage which it may produce, provided it be without altering the
substance of the thing.
     2. The obligation of not altering the substance of the thing, however,
takes place only in the case of a complete usufruct.
     3. Usufructs are of two kinds; perfect and imperfect. Perfect usufruct,
which is of things which the usufructuary can enjoy without altering their
substance, though their substance may be diminished or deteriorated
naturally by time or by the use to which they are applied; as a house, a
piece of land, animals, furniture and other movable effects. Imperfect or
quasi usufruct, which is of things which would be useless to the
usufructuary if be did not consume and expend them, or change the substance
of them, as money, grain, liquors. Civ. Code of Louis. art. 525, et seq.; 1
Browne's Civ. Law, 184; Poth. Tr. du Douaire, n. 194; Ayl. Pand. 319; Poth.
Pand. tom. 6, p. 91; Lecons El. du Dr. Civ. Rom. 414 Inst. lib. 2, t. 4;
Dig. lib. 7, t. 1, 1. 1 Code, lib. 3, t. 33; 1 Bouv. Inst. Theolo. pg. 1, c.
1, art. 2, p. 76.