The Collaborative International Dictionary of English v.0.48:

Muff \Muff\ (m[u^]f), n. [Cf. LG. muff, D. mof, G., Dan., & Sw.
   muff, F. moufle mitten, LL. muffula, MHG. mouwe sleeve, D.
   mouw, and E. muffle, v.]
   1. A soft cover of cylindrical form, usually of fur, worn by
      women to shield the hands from cold.
      [1913 Webster]

   2. (Mech.) A short hollow cylinder surrounding an object, as
      a pipe.
      [1913 Webster]

   3. (Glass Manuf.) A blown cylinder of glass which is
      afterward flattened out to make a sheet.
      [1913 Webster]

   4. [Perhaps a different word; cf. Prov. E. maffle to
      slammer.] A stupid fellow; a poor-spirited person.
      [Colloq.] "A muff of a curate." --Thackeray.
      [1913 Webster]

   5. [See 4.] (Baseball) A failure to hold a ball when once in
      the hands.
      [1913 Webster]

   6. (Zool.) The whitethroat. [Prov. Eng.]
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Muff \Muff\, v. t. [imp. & p. p. Muffed; p. pr. & vb. n.
   Muffing.]
   To handle awkwardly; to fumble; to fail to hold, as a ball,
   in catching it.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Whitethroat \White"throat`\, n. (Zool.)
   Any one of several species of Old World warblers, esp. the
   common European species (Sylvia cinerea), called also
   strawsmear, nettlebird, muff, and whitecap, the
   garden whitethroat, or golden warbler (Sylvia
   hortensis), and the lesser whitethroat (Sylvia curruca).
   [1913 Webster]

WordNet (r) 3.0 (2006):

muff
    n 1: a warm tubular covering for the hands
    2: (sports) dropping the ball [syn: fumble, muff]
    v 1: fail to catch, as of a ball
    2: make a mess of, destroy or ruin; "I botched the dinner and we
       had to eat out"; "the pianist screwed up the difficult
       passage in the second movement" [syn: botch, bodge,
       bumble, fumble, botch up, muff, blow, flub,
       screw up, ball up, spoil, muck up, bungle, fluff,
       bollix, bollix up, bollocks, bollocks up, bobble,
       mishandle, louse up, foul up, mess up, fuck up]

Moby Thesaurus II by Grady Ward, 1.0:

66 Moby Thesaurus words for "muff":
   bad job, be all thumbs, bevue, blow, blunder, blunder away,
   blunder into, blunder on, blunder upon, bobble, boggle, bollix,
   bonehead play, boner, boo-boo, botch, bumble, bungle, butcher,
   butterfingers, clumsy, clumsy performance, commit a gaffe, dub,
   duffer, error, etourderie, faux pas, flounder, flub, fluff, foozle,
   foozler, foul-up, fumble, fumble-fist, gaucherie, goof, goof up,
   goofball, goofer, hash, hick, louse up, lumber, lummox, lump, mar,
   mess, miscue, mistake, muddle, muffer, murder, off day,
   play havoc with, rube, sad work, screw up, slip, slob, spoil,
   stumble, stumblebum, stumblebunny, trip