dumb·found also dum·found 
(dŭmfound′)
(dŭmfound′)tr.v. dumb·found·ed, dumb·found·ing, dumb·founds also dum·found·ed or dum·found·ing or dum·founds
To fill with astonishment and perplexity; confound. See Synonyms at surprise.
[DUMB + (CON)FOUND.]