Source : Webster's Revised Unabridged Dictionary (1913)

Thumb \Thumb\, v. t. [imp. & p. p. {Thumbed}; p. pr. & vb. n.
   {Thumbing}.]
   1. To handle awkwardly. --Johnson.

   2. To play with the thumbs, or with the thumbs and fingers;
      as, to thumb over a tune.

   3. To soil or wear with the thumb or the fingers; to soil, or
      wear out, by frequent handling; also, to cover with the
      thumb; as, to thumb the touch-hole of a cannon.

            He gravely informed the enemy that all his cards had
            been thumbed to pieces, and begged them to let him
            have a few more packs.                --Macaulay.

Thumb \Thumb\, n. [OE. thombe, thoumbe, [thorn]ume, AS.
   [thorn][=u]ma; akin to OFries. th[=u]ma, D. duim, G. daumen,
   OHG. d[=u]mo, Icel. [thorn]umall, Dan. tommelfinger, Sw.
   tumme, and perhaps to L. tumere to swell. [root]56. Cf.
   {Thimble}, {Tumid}.]
   The short, thick first digit of the human hand, differing
   from the other fingers in having but two phalanges; the
   pollex. See {Pollex}.

         Upon his thumb he had of gold a ring.    --Chaucer.

   {Thumb band}, a twist of anything as thick as the thumb.
      --Mortimer.

   {Thumb blue}, indigo in the form of small balls or lumps,
      used by washerwomen to blue linen, and the like.

   {Thumb latch}, a door latch having a lever formed to be
      pressed by the thumb.

   {Thumb mark}.
   (a) The mark left by the impression of a thumb, as on the
       leaves of a book. --Longfellow.
   (b) The dark spot over each foot in finely bred black and tan
       terriers.

   {Thumb nut}, a nut for a screw, having wings to grasp between
      the thumb and fingers in turning it; also, a nut with a
      knurled rim for the same perpose.

   {Thumb ring}, a ring worn on the thumb. --Shak.

   {Thumb stall}.
   (a) A kind of thimble or ferrule of iron, or leather, for
       protecting the thumb in making sails, and in other work.
   (b) (Mil.) A buckskin cushion worn on the thumb, and used to
       close the vent of a cannon while it is sponged, or
       loaded.

   {Under one's thumb}, completely under one's power or
      influence; in a condition of subservience. [Colloq.]

Thumb \Thumb\, v. i.
   To play with the thumb or thumbs; to play clumsily; to thrum.

Source : WordNet®

thumb
     v 1: travel by getting free rides from motorists [syn: {hitchhike},
           {hitch}]
     2: look through a book or other written material; "He thumbed
        through the report"; "She leafed through the volume" [syn:
         {flick}, {flip}, {riffle}, {leaf}, {riff}]
     3: feel or handle with the fingers; "finger the binding of the
        book" [syn: {finger}]

thumb
     n 1: the thick short innermost digit of the forelimb [syn: {pollex}]
     2: the part of a glove that provides a covering for the thumb
     3: a convex molding having a cross section in the form of a
        quarter of a circle or of an ellipse [syn: {ovolo}, {quarter
        round}]

Source : Free On-Line Dictionary of Computing

thumb
     
         The slider or "bubble" on a window system
        {scrollbar}.  So called because moving it allows you to browse
        through the contents of a text window in a way analogous to
        thumbing through a book.
     
        [{Jargon File}]
     
        (1995-03-14)

Thumb
     
         An extension to the {Advanced RISC Machine}
        architecture, announced on 06 March 1995 by {Advanced RISC
        Machines} Ltd.  By identifying the critical subset of the ARM
        {instruction set} and encoding it into 16 bits, ARM has
        succeeded in reducing typical program size by 30-40% from
        ARM's already excellent code density.  Since this Thumb
        instruction set uses less memory for program storage, cost is
        further reduced.
     
        All Thumb-aware {processor core}s combine the capability to
        execute both the 32-bit ARM and the 16-bit Thumb instruction
        sets.  Careful design of the Thumb instructions allow them to
        be decompressed into full ARM instructions transparently
        during normal instruction decoding without any performance
        penalty.  This differs from other 32-bit processors, like the
        {Intel 486SX}, with a 16-bit data bus, which require two
        16-bit memory accesses to execute every 32-bit instruction and
        so halve performance.
     
        The patented Thumb decompressor has been carefully designed
        with only a small amount of circuitry additional to the
        existing instruction decoder, so chip size and thus cost do
        not significantly increase.  Designers can easily interleave
        fast ARM instructions (for performance critical parts of a
        program) with compact Thumb code to save memory.
     
        (1995-03-14)