The Collaborative International Dictionary of English v.0.48:

Commentary \Com"men*ta*ry\, n.; pl. Commentaries. [L.
   commentarius, commentarium, note book, commentary: cf. F.
   commentaire. See Comment, v. i.]
   1. A series of comments or annotations; esp., a book of
      explanations or expositions on the whole or a part of the
      Scriptures or of some other work.
      [1913 Webster]

            This letter . . . was published by him with a severe
            commentary.                           --Hallam.
      [1913 Webster]

   2. A brief account of transactions or events written hastily,
      as if for a memorandum; -- usually in the plural; as,
      Caesar's Commentaries on the Gallic War.
      [1913 Webster]

WordNet (r) 3.0 (2006):

commentary
    n 1: a written explanation or criticism or illustration that is
         added to a book or other textual material; "he wrote an
         extended comment on the proposal" [syn: comment,
         commentary]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "commentary":
   affix, allonge, analysis, annotation, apparatus criticus, appendix,
   coda, codicil, comment, commentation, critical review, criticism,
   critique, editorial, enclitic, envoi, epilogue, exegesis, footnote,
   gloss, infix, interlineation, interpolation, leader,
   leading article, marginalia, notation, note, note of explanation,
   notice, obiter dictum, observation, postscript, prefix, proclitic,
   remark, report, review, rider, running commentary, scholia,
   scholium, suffix, tail, word of explanation, write-up