The Collaborative International Dictionary of English v.0.48:

Compound \Com"pound\, a. [OE. compouned, p. p. of compounen. See
   Compound, v. t.]
   Composed of two or more elements, ingredients, parts;
   produced by the union of several ingredients, parts, or
   things; composite; as, a compound word.
   [1913 Webster]

         Compound substances are made up of two or more simple
         substances.                              --I. Watts.
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   Compound addition, subtraction, multiplication,
   division (Arith.), the addition, subtraction, etc., of
      compound numbers.

   Compound crystal (Crystallog.), a twin crystal, or one
      seeming to be made up of two or more crystals combined
      according to regular laws of composition.

   Compound engine (Mech.), a form of steam engine in which
      the steam that has been used in a high-pressure cylinder
      is made to do further service in a larger low-pressure
      cylinder, sometimes in several larger cylinders,
      successively.

   Compound ether. (Chem.) See under Ether.

   Compound flower (Bot.), a flower head resembling a single
      flower, but really composed of several florets inclosed in
      a common calyxlike involucre, as the sunflower or
      dandelion.

   Compound fraction. (Math.) See Fraction.

   Compound fracture. See Fracture.

   Compound householder, a householder who compounds or
      arranges with his landlord that his rates shall be
      included in his rents. [Eng.]

   Compound interest. See Interest.

   Compound larceny. (Law) See Larceny.

   Compound leaf (Bot.), a leaf having two or more separate
      blades or leaflets on a common leafstalk.

   Compound microscope. See Microscope.

   Compound motion. See Motion.

   Compound number (Math.), one constructed according to a
      varying scale of denomination; as, 3 cwt., 1 qr., 5 lb.;
      -- called also denominate number.

   Compound pier (Arch.), a clustered column.

   Compound quantity (Alg.), a quantity composed of two or
      more simple quantities or terms, connected by the sign +
      (plus) or - (minus). Thus, a + b - c, and bb - b, are
      compound quantities.

   Compound radical. (Chem.) See Radical.

   Compound ratio (Math.), the product of two or more ratios;
      thus ab:cd is a ratio compounded of the simple ratios a:c
      and b:d.

   Compound rest (Mech.), the tool carriage of an engine
      lathe.

   Compound screw (Mech.), a screw having on the same axis two
      or more screws with different pitch (a differential
      screw), or running in different directions (a right and
      left screw).

   Compound time (Mus.), that in which two or more simple
      measures are combined in one; as, 6-8 time is the joining
      of two measures of 3-8 time.

   Compound word, a word composed of two or more words;
      specifically, two or more words joined together by a
      hyphen.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Interest \In"ter*est\, n. [OF. interest, F. int['e]r[^e]t, fr.
   L. interest it interests, is of interest, fr. interesse to be
   between, to be difference, to be importance; inter between +
   esse to be; cf. LL. interesse usury. See Essence.]
   [1913 Webster]
   1. Excitement of feeling, whether pleasant or painful,
      accompanying special attention to some object; concern; a
      desire to learn more about a topic or engage often in an
      activity.
      [1913 Webster +PJC]

   Note: Interest expresses mental excitement of various kinds
         and degrees. It may be intellectual, or sympathetic and
         emotional, or merely personal; as, an interest in
         philosophical research; an interest in human suffering;
         the interest which an avaricious man takes in money
         getting.
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               So much interest have I in thy sorrow. --Shak.
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   2. (Finance, Commerce) Participation in advantage, profit,
      and responsibility; share; portion; part; as, an interest
      in a brewery; he has parted with his interest in the
      stocks.
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   3. Advantage, personal or general; good, regarded as a
      selfish benefit; profit; benefit.
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            Divisions hinder the common interest and public
            good.                                 --Sir W.
                                                  Temple.
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            When interest calls of all her sneaking train.
                                                  --Pope.
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   4. (Finance) A fee paid for the use of money; a fee paid for
      a loan; -- usually reckoned as a percentage; as, interest
      at five per cent per annum on ten thousand dollars.
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            They have told their money, and let out
            Their coin upon large interest.       --Shak.
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   5. Any excess of advantage over and above an exact equivalent
      for what is given or rendered.
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            You shall have your desires with interest. --Shak.
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   6. The persons interested in any particular business or
      measure, taken collectively; as, the iron interest; the
      cotton interest.
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   Compound interest, interest, not only on the original
      principal, but also on unpaid interest from the time it
      fell due.

   Simple interest, interest on the principal sum without
      interest on overdue interest.
      [1913 Webster]

WordNet (r) 3.0 (2006):

compound interest
    n 1: interest calculated on both the principal and the accrued
         interest

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

COMPOUND INTEREST. Interest allowed upon interest; for example, when a sum
of money due for interest, is added to the principal, and then bears
interest. This is not, in general, allowed. See Interest for money.