The Collaborative International Dictionary of English v.0.48:

Advocate \Ad"vo*cate\, v. t. [imp. & p. p. Advocated; p. pr. &
   vb. n. Advocating.] [See Advocate, n., Advoke, Avow.]
   To plead in favor of; to defend by argument, before a
   tribunal or the public; to support, vindicate, or recommend
   publicly.
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         To advocate the cause of thy client.     --Bp.
                                                  Sanderson
                                                  (1624).
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         This is the only thing distinct and sensible, that has
         been advocated.                          --Burke.
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         Eminent orators were engaged to advocate his cause.
                                                  --Mitford.
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The Collaborative International Dictionary of English v.0.48:

Advocate \Ad"vo*cate\, n. [OE. avocat, avocet, OF. avocat, fr.
   L. advocatus, one summoned or called to another; properly the
   p. p. of advocare to call to, call to one's aid; ad + vocare
   to call. See Advowee, Avowee, Vocal.]
   1. One who pleads the cause of another. Specifically: One who
      pleads the cause of another before a tribunal or judicial
      court; a counselor.
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   Note: In the English and American Law, advocate is the same
         as "counsel," "counselor," or "barrister." In the civil
         and ecclesiastical courts, the term signifies the same
         as "counsel" at the common law.
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   2. One who defends, vindicates, or espouses any cause by
      argument; a pleader; as, an advocate of free trade, an
      advocate of truth.
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   3. Christ, considered as an intercessor.
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            We have an Advocate with the Father.  --1 John ii.
                                                  1.
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   Faculty of advocates (Scot.), the Scottish bar in
      Edinburgh.

   Lord advocate (Scot.), the public prosecutor of crimes, and
      principal crown lawyer.

   Judge advocate. See under Judge.
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The Collaborative International Dictionary of English v.0.48:

Advocate \Ad"vo*cate\, v. i.
   To act as advocate. [Obs.] --Fuller.
   [1913 Webster]

WordNet (r) 3.0 (2006):

advocate
    n 1: a person who pleads for a cause or propounds an idea [syn:
         advocate, advocator, proponent, exponent]
    2: a lawyer who pleads cases in court [syn: advocate,
       counsel, counselor, counsellor, counselor-at-law,
       pleader]
    v 1: push for something; "The travel agent recommended strongly
         that we not travel on Thanksgiving Day" [syn: recommend,
         urge, advocate]
    2: speak, plead, or argue in favor of; "The doctor advocated a
       smoking ban in the entire house" [syn: preach, advocate]