The Collaborative International Dictionary of English v.0.48:

Interest \In"ter*est\, v. t. [imp. & p. p. Interested; p. pr.
   & vb. n. Interesting.] [From interess'd, p. p. of the older
   form interess, fr. F. int['e]resser, L. interesse. See
   Interest, n.]
   [1913 Webster]
   1. To engage the attention of; to awaken interest in; to
      excite emotion or passion in, in behalf of a person or
      thing; as, the subject did not interest him; to interest
      one in charitable work.
      [1913 Webster]

            To love our native country . . . to be interested in
            its concerns is natural to all men.   --Dryden.
      [1913 Webster]

            A goddess who used to interest herself in marriages.
                                                  --Addison.
      [1913 Webster]

   2. To be concerned with or engaged in; to affect; to concern;
      to excite; -- often used impersonally. [Obs.]
      [1913 Webster]

            Or rather, gracious sir,
            Create me to this glory, since my cause
            Doth interest this fair quarrel.      --Ford.
      [1913 Webster]

   3. To cause or permit to share. [Obs.]
      [1913 Webster]

            The mystical communion of all faithful men is such
            as maketh every one to be interested in those
            precious blessings which any one of them receiveth
            at God's hands.                       --Hooker.

   Syn: To concern; excite; attract; entertain; engage; occupy;
        hold.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Interested \In"ter*est*ed\ ([i^]n"t[~e]r*[e^]st*[e^]d), a. [See
   Interest, v. t.]
   [1913 Webster]
   1. Having the attention engaged; having emotion or passion
      excited; as, an interested listener.
      [1913 Webster]

   2. Having an interest; concerned in a cause or in
      consequences; liable to be affected or prejudiced; as, an
      interested witness; an interested party.
      [1913 Webster]

WordNet (r) 3.0 (2006):

interested
    adj 1: having or showing interest; especially curiosity or
           fascination or concern; "an interested audience";
           "interested in sports"; "was interested to hear about her
           family"; "interested in knowing who was on the
           telephone"; "interested spectators" [ant: uninterested]
    2: involved in or affected by or having a claim to or share in;
       "a memorandum to those concerned"; "an enterprise in which
       three men are concerned"; "factors concerned in the rise and
       fall of epidemics"; "the interested parties met to discuss
       the business" [syn: concerned, interested]