The Collaborative International Dictionary of English v.0.48:

Tumbler \Tum"bler\, n.
   1. One who tumbles; one who plays tricks by various motions
      of the body; an acrobat.
      [1913 Webster]

   2. A movable obstruction in a lock, consisting of a lever,
      latch, wheel, slide, or the like, which must be adjusted
      to a particular position by a key or other means before
      the bolt can be thrown in locking or unlocking.
      [1913 Webster]

   3. (Firearms) A piece attached to, or forming part of, the
      hammer of a gunlock, upon which the mainspring acts and in
      which are the notches for the sear point to enter.
      [1913 Webster]

   4. A drinking glass, without a foot or stem; -- so called
      because originally it had a pointed or convex base, and
      could not be set down with any liquor in it, thus
      compelling the drinker to finish his measure.
      [1913 Webster]

   5. (Zool.) A variety of the domestic pigeon remarkable for
      its habit of tumbling, or turning somersaults, during its
      flight.
      [1913 Webster]

   6. (Zool.) A breed of dogs that tumble when pursuing game.
      They were formerly used in hunting rabbits.
      [1913 Webster]

   7. A kind of cart; a tumbrel. [Prov. Eng. & Scot.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

tumbler
    n 1: a gymnast who performs rolls and somersaults and twists
         etc.
    2: a glass with a flat bottom but no handle or stem; originally
       had a round bottom
    3: a movable obstruction in a lock that must be adjusted to a
       given position (as by a key) before the bolt can be thrown
    4: pigeon that executes backward somersaults in flight or on the
       ground [syn: roller, tumbler, tumbler pigeon]

Moby Thesaurus II by Grady Ward, 1.0:

25 Moby Thesaurus words for "tumbler":
   acrobat, aerialist, bareback rider, circus artist, clown,
   contortionist, equestrian director, equilibrist, flier,
   funambulist, gymnast, high wire artist, high-wire artist, juggler,
   lion tamer, palaestrian, pancratiast, ringmaster, ropewalker,
   slack-rope artist, snake charmer, sword swallower,
   tightrope walker, trapeze artist, weightlifter



The Jargon File (version 4.4.7, 29 Dec 2003):

tumbler
 n.

    1. [Originally from the Xanadu hypertext project] A tumbler is a magic
    cookie generated as part of a record or message to give it a unique
    identity. Usually a tumbler includes an encoded form of its creation date,
    but if a software system has more than one concurrent process that could
    generate tumblers it must also include an encoding of the process ID. If
    tumblers will be shared across multiple network hosts, they must also
    include the host name or network address. Tumblers often include a hash of
    the rest of the message or record content so that it is possible to verify
    the correctness of the data the tumbler is attached to.

    2. Variant text added to spam instances (often in the Subject line) to make
    them unique. This kind of tumbler is used to defeat schemes that check an
    exact hash of an incoming message against known spam signatures; it also
    compromises some kinds of statistical spam recognition.