The Collaborative International Dictionary of English v.0.48:

Apology \A*pol"o*gy\, n.; pl. Apologies. [L. apologia, Gr. ?;
   ? from + ?: cf. F. apologie. See Apologetic.]
   1. Something said or written in defense or justification of
      what appears to others wrong, or of what may be liable to
      disapprobation; justification; as, Tertullian's Apology
      for Christianity.
      [1913 Webster]

            It is not my intention to make an apology for my
            poem; some will think it needs no excuse, and others
            will receive none.                    --Dryden.
      [1913 Webster]

   2. An acknowledgment intended as an atonement for some
      improper or injurious remark or act; an admission to
      another of a wrong or discourtesy done him, accompanied by
      an expression of regret.
      [1913 Webster]

   3. Anything provided as a substitute; a makeshift.
      [1913 Webster]

            He goes to work devising apologies for window
            curtains.                             --Dickens.
      [1913 Webster]

   Syn: Excuse.

   Usage: An apology, in the original sense of the word, was a
          pleading off from some charge or imputation, by
          explaining and defending one's principles or conduct.
          It therefore amounted to a vindication. One who offers
          an apology, admits himself to have been, at least
          apparently, in the wrong, but brings forward some
          palliating circumstance, or tenders a frank
          acknowledgment, by way of reparation. We make an
          apology for some breach of propriety or decorum (like
          rude expressions, unbecoming conduct, etc.), or some
          deficiency in what might be reasonably expected. We
          offer an excuse when we have been guilty of some
          breach or neglect of duty; and we do it by way of
          extenuating our fault, and with a view to be forgiven.
          When an excuse has been accepted, an apology may
          still, in some cases, be necessary or appropriate. "An
          excuse is not grounded on the claim of innocence, but
          is rather an appeal for favor resting on some
          collateral circumstance. An apology mostly respects
          the conduct of individuals toward each other as
          equals; it is a voluntary act produced by feelings of
          decorum, or a desire for the good opinion of others."
          --Crabb.
          [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Apology \A*pol"o*gy\, v. i.
   To offer an apology. [Obs.]
   [1913 Webster]

         For which he can not well apology.       --J. Webster.
   [1913 Webster]

WordNet (r) 3.0 (2006):

apology
    n 1: an expression of regret at having caused trouble for
         someone; "he wrote a letter of apology to the hostess"
    2: a formal written defense of something you believe in strongly
       [syn: apology, apologia]
    3: a poor example; "it was an apology for a meal"; "a poor
       excuse for an automobile" [syn: apology, excuse]

Moby Thesaurus II by Grady Ward, 1.0:

116 Moby Thesaurus words for "apology":
   abject apology, acknowledgment, admission, advocating, advocation,
   alibi, amends, apologetic, apologetics, apologia, apologies,
   argument, argumentation, atonement, attrition, ayenbite of inwit,
   bicker, bickering, bitterness, blind, breast-beating, casuistry,
   championing, change of heart, cloak, color, concession, confession,
   contention, contriteness, contrition, controversy, cover,
   cover story, cover-up, deathbed repentance, defense, device,
   disputation, dispute, espousal, excuse, extenuation, facade, feint,
   flyting, front, gloss, grief, guise, handle, hassle,
   heartfelt apology, hubbub, justification, lame excuse, litigation,
   locus standi, logomachy, mask, mea culpa, ostensible motive,
   palliation, paper war, passage of arms, penance, penitence,
   polemic, polemics, poor excuse, pretense, pretension, pretext,
   protestation, public motive, put-off, redress, reformation, refuge,
   regret, regretfulness, regrets, regretting, remorse,
   remorse of conscience, remorsefulness, reparation, repentance,
   repining, rhubarb, saeta, satisfaction, screen, semblance, set-to,
   sham, shame, shamefacedness, shamefastness, shamefulness, show,
   smoke screen, sorriness, sorrow, stalking-horse, stratagem,
   subterfuge, support, trick, varnish, veil, verbal engagement,
   war of words, wearing a hairshirt, wistfulness, wrangling