The Collaborative International Dictionary of English v.0.48:

Encumber \En*cum"ber\, v. t. [imp. & p. p. Encumbered; p. pr.
   & vb. n. Encumbering.] [F. encombrer; pref. en- (L. in) +
   OF. combrer to hinder. See Cumber, and cf. Incumber.]
   [Written also incumber.]
   1. To impede the motion or action of, as with a burden; to
      retard with something superfluous; to weigh down; to
      obstruct or embarrass; as, his movements were encumbered
      by his mantle; his mind is encumbered with useless
      learning.
      [1913 Webster]

            Not encumbered with any notable inconvenience.
                                                  --Hooker.
      [1913 Webster]

   2. To load with debts, or other legal claims; as, to encumber
      an estate with mortgages.

   Syn: To load; clog; oppress; overload; embarrass; perplex;
        hinder; retard; obstruct; check; block.
        [1913 Webster]

WordNet (r) 3.0 (2006):

encumbered
    adj 1: loaded to excess or impeded by a heavy load; "a summer
           resort...encumbered with great clapboard-and-stucco
           hotels"- A.J.Liebling; "a hiker encumbered with a heavy
           backpack"; "an encumbered estate" [ant: unencumbered]

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "encumbered":
   burdened, burdened with debt, charged, cumbered, deep in debt,
   embarrassed, fraught, freighted, hampered, in debt,
   in difficulties, in embarrassed circumstances, in hock,
   in the hole, in the red, indebted, involved, laden, loaded,
   mortgaged, oppressed, overburdened, overcharged, overfraught,
   overfreighted, overladen, overloaded, overtaxed, overweighted,
   plunged in debt, saddled, taxed, tied up, weighted,
   weighted down