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]

WordNet (r) 3.0 (2006):

cluttered
    adj 1: filled or scattered with a disorderly accumulation of
           objects or rubbish; "the storm left the drivewaylittered
           with sticks nd debris"; "his library was a cluttered room
           with piles of books on every chair" [syn: cluttered,
           littered]