Source : Webster's Revised Unabridged Dictionary (1913)

Thud \Thud\, v. i. & t.
   To make, or strike so as to make, a dull sound, or thud.

         Hardly the softest thudding of velvety pads. --A. C.
                                                  Doyle.

         The waves break into spray, dash and rumble and thud
         below your feet.                         --H. F. Brown.

Thud \Thud\ (th[u^]d), n. [Cf. AS. [thorn][=o]den a whirlwind,
   violent wind, or E. thump.]
   A dull sound without resonance, like that produced by
   striking with, or striking against, some comparatively soft
   substance; also, the stroke or blow producing such sound; as,
   the thrud of a cannon ball striking the earth.

         At every new thud of the blast, a sob arose. --Jeffrey.

         At intervals there came some tremendous thud on the
         side of the steamer.                     --C. Mackay.

Source : WordNet®

thud
     n : a heavy dull sound (as made by impact of heavy objects)
         [syn: {thump}, {thumping}, {clump}, {clunk}]
     v 1: make a dull sound; "the knocker thudded against the front
          door" [syn: {thump}]
     2: strike with a dull sound; "Bullets were thudding against the
        wall"
     3: make a noise typical of an engine lacking lubricants [syn: {crump},
         {scrunch}]
     [also: {thudding}, {thudded}]

Source : Free On-Line Dictionary of Computing

thud
     
        1. Yet another {metasyntactic variable} (see {foo}).  It is
        reported that at {CMU} from the mid-1970s the canonical series
        of these was "foo", "bar", "thud", "blat".
     
        2. Rare term for the hash character, "#" (ASCII 35).  See
        {ASCII} for other synonyms.
     
        [{Jargon File}]