The Collaborative International Dictionary of English v.0.48:

acknowledge \ac*knowl"edge\ ([a^]k*n[o^]l"[e^]j), v. t. [imp. &
   p. p. acknowledged ([a^]k*n[o^]l"[e^]jd); p. pr. & vb. n.
   acknowledging ([a^]k*n[o^]l"[e^]j*[i^]ng).] [Prob. fr.
   pref. a- + the verb knowledge. See Knowledge, and cf.
   Acknow.]
   1. To own or admit the knowledge of; to recognize as a fact
      or truth; to declare one's belief in; as, to acknowledge
      the being of a God.
      [1913 Webster]

            I acknowledge my transgressions.      --Ps. li. 3.
      [1913 Webster]

            For ends generally acknowledged to be good.
                                                  --Macaulay.
      [1913 Webster]

   2. To own or recognize in a particular character or
      relationship; to admit the claims or authority of; to give
      recognition to.
      [1913 Webster]

            In all thy ways acknowledge Him.      --Prov. iii.
                                                  6.
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            By my soul, I'll ne'er acknowledge thee. --Shak.
      [1913 Webster]

   3. To own with gratitude or as a benefit or an obligation;
      as, to acknowledge a favor, the receipt of a letter.
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            They his gifts acknowledged none.     --Milton.
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   4. To own as genuine; to assent to, as a legal instrument, to
      give it validity; to avow or admit in legal form; as, to
      acknowledge a deed.
      [1913 Webster]

   Syn: To avow; proclaim; recognize; own; admit; allow;
        concede; confess.

   Usage: Acknowledge, Recognize. Acknowledge is opposed to
          keep back, or conceal, and supposes that something had
          been previously known to us (though perhaps not to
          others) which we now feel bound to lay open or make
          public. Thus, a man acknowledges a secret marriage;
          one who has done wrong acknowledges his fault; and
          author acknowledges his obligation to those who have
          aided him; we acknowledge our ignorance. Recognize
          supposes that we have either forgotten or not had the
          evidence of a thing distinctly before our minds, but
          that now we know it (as it were) anew, or receive and
          admit in on the ground of the evidence it brings.
          Thus, we recognize a friend after a long absence. We
          recognize facts, principles, truths, etc., when their
          evidence is brought up fresh to the mind; as, bad men
          usually recognize the providence of God in seasons of
          danger. A foreign minister, consul, or agent, of any
          kind, is recognized on the ground of his producing
          satisfactory credentials. See also Confess.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

acknowledged \ac*knowl"edged\ ([a^]k*n[o^]l"[e^]jd) adj.
   Generally accepted or recognized as correct or reasonable.
   Opposite of unacknowledged. [Narrower terms: given,
   granted; unquestionable (vs. questionable)] Also See:
   known.

   Syn: accepted, recognized
        [WordNet 1.5 +PJC]

WordNet (r) 3.0 (2006):

acknowledged
    adj 1: recognized or made known or admitted; "the acknowledged
           leader of the community"; "a woman of acknowledged
           accomplishments"; "his acknowledged error" [ant:
           unacknowledged]
    2: generally accepted

Moby Thesaurus II by Grady Ward, 1.0:

68 Moby Thesaurus words for "acknowledged":
   accepted, admitted, affirmed, allowed, approved, authenticated,
   avowed, being done, certified, comme il faut, conceded, confessed,
   confirmed, conformable, conventional, correct, countersigned,
   customary, de rigueur, decent, decorous, endorsed, established,
   fixed, folk, formal, granted, hallowed, handed down, heroic, hoary,
   immemorial, inveterate, legendary, long-established, long-standing,
   meet, mythological, notarized, of long standing, of the folk, oral,
   orthodox, prescriptive, professed, proper, ratified, received,
   recognized, right, rooted, sealed, seemly, signed, stamped,
   sworn and affirmed, sworn to, time-honored, traditional,
   tried and true, true-blue, understood, underwritten, unwritten,
   validated, venerable, warranted, worshipful