The Collaborative International Dictionary of English v.0.48:

Pack \Pack\, n. [Akin to D. pak, G. pack, Dan. pakke, Sw. packa,
   Icel. pakki, Gael. & Ir. pac, Arm. pak. Cf. Packet.]
   [1913 Webster]
   1. A bundle made up and prepared to be carried; especially, a
      bundle to be carried on the back; a load for an animal; a
      bale, as of goods. --Piers Plowman.
      [1913 Webster]

   2. [Cf. Peck, n.] A number or quantity equal to the
      contents of a pack; hence, a multitude; a burden. "A pack
      of sorrows." "A pack of blessings." --Shak.
      [1913 Webster]

   Note: "In England, by a pack of meal is meant 280 lbs.; of
         wool, 240 lbs." --McElrath.
         [1913 Webster]

   3. A group or quantity of connected or similar things; as, a
      pack of lies; specifically:
      (a) A full set of playing cards; a deck; also, the
          assortment used in a particular game; as, a euchre
          pack.
      (b) A number of wolves, hounds or dogs, hunting or kept
          together; as, a wolf pack.
      (c) A number of persons associated or leagued in a bad
          design or practice; a gang; as, a pack of thieves or
          knaves.
      (d) A shook of cask staves.
      (e) A bundle of sheet-iron plates for rolling
          simultaneously.
          [1913 Webster]

   4. A large area of floating pieces of ice driven together
      more or less closely. --Kane.
      [1913 Webster]

   5. An envelope, or wrapping, of sheets used in hydropathic
      practice, called dry pack, wet pack, cold pack,
      etc., according to the method of treatment.
      [1913 Webster]

   6. [Prob. the same word; but cf. AS. p[=ae]can to deceive.] A
      loose, lewd, or worthless person. See Baggage. [Obs.]
      --Skelton.
      [1913 Webster]

   7. (Med.) In hydropathic practice, a wrapping of blankets or
      sheets called dry pack, wet pack, cold pack, etc.,
      according to the condition of the blankets or sheets used,
      put about a patient to give him treatment; also, the fact
      or condition of being so treated.
      [Webster 1913 Suppl.]

   8. (Rugby Football) The forwards who compose one half of the
      scrummage; also, the scrummage.
      [Webster 1913 Suppl.]

   Pack animal, an animal, as a horse, mule, etc., employed in
      carrying packs.

   Pack and prime road or Pack and prime way, a pack road or
      bridle way.

   Pack cloth, a coarse cloth, often duck, used in covering
      packs or bales.

   Pack horse. See Pack animal (above).

   Pack ice. See def. 4, above.

   Pack moth (Zool.), a small moth (Anacampsis sarcitella)
      which, in the larval state, is very destructive to wool
      and woolen fabrics.

   Pack needle, a needle for sewing with pack thread. --Piers
      Plowman.

   Pack saddle, a saddle made for supporting the load on a
      pack animal. --Shak.

   Pack staff, a staff for supporting a pack; a peddler's
      staff.

   Pack train (Mil.), a troop of pack animals.
      [1913 Webster]

WordNet (r) 3.0 (2006):

pack animal
    n 1: an animal (such as a mule or burro or horse) used to carry
         loads [syn: pack animal, sumpter]