The Collaborative International Dictionary of English v.0.48:

Muffle \Muf"fle\, v. t. [imp. & p. p. Muffled; p. pr. & vb. n.
   Muffling.] [Cf. F. moufle a mitten, LL. muffula, OD. moffel
   a muff. See Muff.]
   1. To wrap up in something that conceals or protects; to
      wrap, as the face and neck, in thick and disguising folds;
      hence, to conceal or cover the face of; to envelop; to
      inclose; -- often with up. --South.
      [1913 Webster]

            The face lies muffled up within the garment.
                                                  --Addison.
      [1913 Webster]

            He muffled with a cloud his mournful eyes. --Dryden.
      [1913 Webster]

            Muffled up in darkness and superstition.
                                                  --Arbuthnot.
      [1913 Webster]

   2. To prevent seeing, or hearing, or speaking, by wraps bound
      about the head; to blindfold; to deafen.
      [1913 Webster]

   3. To wrap or fit with something that dulls or deadens the
      sound of; as, to muffle the strings of a drum, or that
      part of an oar which rests in the rowlock; to muffle the
      exhaust of a motor vehicle.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

muffled \muffled\ adj.
   1. same as muted; as, muffled drums; the muffled noises of
      the street.

   Syn: dull, muted, softened.
        [WordNet 1.5]

   2. Wrapped up especially for protection or secrecy; as,
      children muffled almost to the eyebrows.
      [WordNet 1.5]

WordNet (r) 3.0 (2006):

muffled
    adj 1: being or made softer or less loud or clear; "the dull
           boom of distant breaking waves"; "muffled drums"; "the
           muffled noises of the street"; "muted trumpets" [syn:
           dull, muffled, muted, softened]
    2: wrapped up especially for protection or secrecy; "children
       muffled almost to the eyebrows"