[1] : The Collaborative International Dictionary of English v.0.48

dumbfound \dumbfound\ v.
   same as dumfound.

   syn: confuse, perplex, throw, fox, befuddle, fuddle, bedevil,
        puzzle, mystify, baffle, bewilder, flummox, stupefy,
        stupify, nonplus, gravel, amaze, trounce, confound, be
        confusing to, make confused.
        wordnet 1.5
see also:
dumfound 

[2] : The Collaborative International Dictionary of English v.0.48

dumfound \dum"found`\, v. t. imp.  p. p. dumfounded; p. pr.
    vb. n. dumfounding.
   to strike dumb; to confuse with astonishment. written also
   dumbfound. --spectator.
   1913 webster
see also:
dumfounded dumfounding dumbfound 

[3] : WordNet (r) 2.0

dumbfound
     v : be a mystery or bewildering to; "this beats me"; "got me--i
         don't know the answer"; "a vexing problem"; "this
         question really stuck me" syn: perplex, vex, stick,
          get, puzzle, mystify, baffle, beat, pose, bewilder,
          flummox, stupefy, nonplus, gravel, amaze
see also:
perplex vex stick get puzzle mystify 
baffle beat pose bewilder flummox 
stupefy nonplus gravel amaze 

[4] : Moby Thesaurus II by Grady Ward, 1.0

51 moby thesaurus words for "dumbfound":
   amaze, astonish, astound, awe, awestrike, bedaze, bedazzle,
   bewilder, boggle, bowl down, bowl over, choke, choke off, confound,
   confuse, daze, dazzle, dumbfounder, flabbergast, floor, gag, hush,
   hush-hush, muffle, muzzle, nonplus, overwhelm, paralyze, perplex,
   petrify, put to silence, quiet, quieten, shock, shush,
   shut down on, silence, soft-pedal, squash, squelch, stagger,
   startle, stifle, still, strike dead, strike dumb,
   strike with wonder, stun, stupefy, surprise, throttle

Dumbfound >> D Words
Dumbfound, definition of term: Dumbfound
dumbfound_pag1.html