The Collaborative International Dictionary of English v.0.48:

Muss \Muss\, n. [Cf. OF. mousche a fly, also, the play called
   muss, fr. L. musca a fly.]
   A scramble, as when small objects are thrown down, to be
   taken by those who can seize them; a confused struggle.
   --Shak.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Muss \Muss\, n.
   A state of confusion or disorder; -- prob. variant of mess,
   but influenced by muss, a scramble. [Colloq. U.S.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Muss \Muss\, v. t. [imp. & p. p. Mussed; p. pr. & vb. n.
   Mussing.]
   To disarrange, as clothing; to rumple; -- often used with up;
   as, the wind mussed up my hair. [Colloq. U.S.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Muss \Muss\, n. [Cf. OE. mus a mouse. See Mouse.]
   A term of endearment. [Obs.] See Mouse. --B. Jonson.
   [1913 Webster]

WordNet (r) 3.0 (2006):

muss
    n 1: a state of confusion and disorderliness; "the house was a
         mess"; "she smoothed the mussiness of the bed" [syn:
         mess, messiness, muss, mussiness]
    v 1: make messy or untidy; "the child mussed up my hair" [syn:
         muss, tussle]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "muss":
   botch, botchery, broil, clutter, derange, disarrange, disarray,
   dishevel, dislocate, disorder, disorganize, donnybrook, fracas,
   fray, free-for-all, hash, knock-down-and-drag-out, litter, melee,
   mess, mess up, misarrange, mix-up, muddle, mull, muss up, ruction,
   ruffle, rumple, scatter, set-to, shambles, tousle