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