The Collaborative International Dictionary of English v.0.48:

Clutter \Clut"ter\, n. [Cf. W. cludair heap, pile, cludeirio to
   heap.]
   1. A confused collection; hence, confusion; disorder; as, the
      room is in a clutter.
      [1913 Webster]

            He saw what a clutter there was with huge, overgrown
            pots, pans, and spits.                --L'Estrange.
      [1913 Webster]

   2. Clatter; confused noise. --Swift.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Clutter \Clut"ter\, v. t. [imp. & p. p. Cluttered; p. pr. &
   vb. n. Cluttering.]
   To crowd together in disorder; to fill or cover with things
   in disorder; to throw into disorder; to disarrange; as, to
   clutter a room.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Clutter \Clut"ter\, v. i.
   To make a confused noise; to bustle.
   [1913 Webster]

         It [the goose] cluttered here, it chuckled there.
                                                  --Tennyson.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Clutter \Clut"ter\, v. t. [From Clod, n.]
   To clot or coagulate, as blood. [Obs.] --Holland.
   [1913 Webster]

WordNet (r) 3.0 (2006):

clutter
    n 1: a confused multitude of things [syn: clutter, jumble,
         muddle, fuddle, mare's nest, welter, smother]
    2: unwanted echoes that interfere with the observation of
       signals on a radar screen
    v 1: fill a space in a disorderly way [syn: clutter, clutter
         up] [ant: clear, unclutter]

Moby Thesaurus II by Grady Ward, 1.0:

108 Moby Thesaurus words for "clutter":
   a mass of, a world of, abound with, army, arsy-varsiness, ataxia,
   atmospheric attenuation, be alive with, bevy, blind spots,
   bristle with, bunch, burst with, chaos, cloud, confusion, covey,
   crawl with, creep with, crowd, deflection, derange, disarrange,
   disarray, dishevel, dislocate, disorder, disorganize, false echoes,
   farrago, flight, flock, flocks, gallimaufry, ground clutter, hail,
   hash, helter-skelter, higgledy-piggledy, hive, hodgepodge, host,
   huddle, hugger-mugger, hysteron proteron, jam, jumble, jungle,
   large amount, legion, litter, lots, macedoine, many, mash,
   masses of, medley, melange, mess, mess up, misarrange, mishmash,
   mob, muchness, muddle, multiply, multitude, muss, muss up, nest,
   numbers, olla podrida, overflow with, pack, plurality,
   pullulate with, quantities, quite a few, refraction, rout, ruck,
   ruffle, rummage, rumple, scatter, scores, scramble, sea clutter,
   shoal, shuffle, snarl, strew, superrefraction, swarm, swarm with,
   tangle, teem with, throng, throng with, tidy sum, topsy-turviness,
   topsy-turvydom, tousle, tumble, turmoil, unholy mess, welter,
   worlds of