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: WordNet® 2.0

thud n. 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 0100011). See {ASCII} for other synonyms.


Source: The Jargon File