The Collaborative International Dictionary of English v.0.48:

Leash \Leash\ (l[=e]sh), n. [OE. lese, lees, leece, OF. lesse,
   F. laisse, LL. laxa, fr. L. laxus loose. See Lax.]
   1. A thong of leather, or a long cord, by which a person may
      hold or restrain an animal, such as a falconer holding his
      hawk, or a courser his dog. For dogs and cats, the leash
      is commonly attached to a collar around the neck of the
      animal.
      [1913 Webster]

            Even like a fawning greyhound in the leash. --Shak.
      [1913 Webster]

   2. (Sporting) A brace and a half; a tierce; three; three
      creatures of any kind, especially greyhounds, foxes,
      bucks, and hares; hence, the number three in general.
      [1913 Webster]

            [I] kept my chamber a leash of days.  --B. Jonson.
      [1913 Webster]

            Then were I wealthier than a leash of kings.
                                                  --Tennyson.
      [1913 Webster]

   3. (Weaving) A string with a loop at the end for lifting warp
      threads, in a loom.
      [1913 Webster]

   To keep (a person) on a short leash to maintain close
      control over the activities of (a person).
      [PJC]

The Collaborative International Dictionary of English v.0.48:

Leash \Leash\, v. t. [imp. & p. p. Leashed; p. pr. & vb. n.
   Leashing.]
   To tie together, or hold, with a leash.
   [1913 Webster]

WordNet (r) 3.0 (2006):

leash
    n 1: restraint consisting of a rope (or light chain) used to
         restrain an animal [syn: leash, tether, lead]
    2: the cardinal number that is the sum of one and one and one
       [syn: three, 3, III, trio, threesome, tierce,
       leash, troika, triad, trine, trinity, ternary,
       ternion, triplet, tercet, terzetto, trey, deuce-
       ace]
    3: a figurative restraint; "asked for a collar on program
       trading in the stock market"; "kept a tight leash on his
       emotions"; "he's always gotten a long leash" [syn: collar,
       leash]
    v 1: fasten with a rope; "rope the bag securely" [syn: rope,
         leash]