The Collaborative International Dictionary of English v.0.48:

Nonsense \Non"sense\, n. [Pref. non- + sense: cf. F. nonsens.]
   1. That which is not sense, or has no sense; words, or
      language, which have no meaning, or which convey no
      intelligible ideas; absurdity.
      [1913 Webster]

   2. Trifles; things of no importance.
      [1913 Webster]

   Nonsense verses, lines made by taking any words which
      occur, but especially certain words which it is desired to
      recollect, and arranging them without reference to
      anything but the measure, so that the rhythm of the lines
      may aid in recalling the remembrance of the words.
      [1913 Webster]

   Syn: Folly; silliness; absurdity; trash; balderdash.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

fiddledeedee \fid"dle*dee*dee`\, interj.
   An exclamatory word or phrase, equivalent to nonsense!
   [Colloq.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

nonsense
    adj 1: having no intelligible meaning; "nonsense syllables"; "a
           nonsensical jumble of words" [syn: nonsense(a),
           nonsensical]
    n 1: a message that seems to convey no meaning [syn: nonsense,
         bunk, nonsensicality, meaninglessness, hokum]
    2: ornamental objects of no great value [syn: folderal,
       falderol, frill, gimcrackery, gimcrack, nonsense,
       trumpery]

The Devil's Dictionary (1881-1906):

NONSENSE, n.  The objections that are urged against this excellent
dictionary.