Source : Webster's Revised Unabridged Dictionary (1913)

Sinking \Sink"ing\,
   a. & n. from {Sink}.

   {Sinking fund}. See under {Fund}.

   {Sinking head} (Founding), a riser from which the mold is fed
      as the casting shrinks. See {Riser}, n., 4.

   {Sinking pump}, a pump which can be lowered in a well or a
      mine shaft as the level of the water sinks.

Fund \Fund\, n. [OF. font, fond, nom. fonz, bottom, ground, F.
   fond bottom, foundation, fonds fund, fr. L. fundus bottom,
   ground, foundation, piece of land. See {Found} to establish.]
   1. An aggregation or deposit of resources from which supplies
      are or may be drawn for carrying on any work, or for
      maintaining existence.

   2. A stock or capital; a sum of money appropriated as the
      foundation of some commercial or other operation
      undertaken with a view to profit; that reserve by means of
      which expenses and credit are supported; as, the fund of a
      bank, commercial house, manufacturing corporation, etc.

   3. pl. The stock of a national debt; public securities;
      evidences (stocks or bonds) of money lent to government,
      for which interest is paid at prescribed intervals; --
      called also {public funds}.

   4. An invested sum, whose income is devoted to a specific
      object; as, the fund of an ecclesiastical society; a fund
      for the maintenance of lectures or poor students; also,
      money systematically collected to meet the expenses of
      some permanent object.

   5. A store laid up, from which one may draw at pleasure; a
      supply; a full provision of resources; as, a fund of
      wisdom or good sense.

            An inexhaustible fund of stories.     --Macaulay.

   {Sinking fund}, the aggregate of sums of money set apart and
      invested, usually at fixed intervals, for the
      extinguishment of the debt of a government, or of a
      corporation, by the accumulation of interest.

Source : WordNet®

sinking fund
     n : a fund accumulated regularly in a separate account and used
         to redeem debt securities