The Collaborative International Dictionary of English v.0.48:

Tether \Teth"er\, v. t. [imp. & p. p. Tethered; p. pr. & vb.
   n. Tethering.]
   To confine, as an animal, with a long rope or chain, as for
   feeding within certain limits.
   [1913 Webster]

         And by a slender cord was tethered to a stone.
                                                  --Wordsworth.
   [1913 Webster]

WordNet (r) 3.0 (2006):

tethered
    adj 1: confined or restricted with or as if with a rope or chain

Moby Thesaurus II by Grady Ward, 1.0:

35 Moby Thesaurus words for "tethered":
   aground, anchored, bound, caught, chained, fast, fastened,
   fettered, fixed, grounded, hampered, handcuffed, held,
   high and dry, impacted, in bonds, in chains, in irons,
   inextricable, ironbound, jammed, manacled, moored, packed,
   shackled, stranded, strapped, stuck, stuck fast, tied, tied down,
   tied up, trammeled, transfixed, wedged