or dum·found·ed. speechless with amazement; astonished or showing astonishment: I smiled at the dumbfounded look on their faces as their eyes widened and their mouths fell slack.

Is dumbfounded a negative word?

Dumbfounded: "greatly astonish or amaze: they were dumbfounded at his popularity." (New Oxford American Dictionary) Although it doesn't necessarily suggest a negative outcome, I think it does generally carry connotations of nonplussed bemusement. As others have already mentioned, there's also appalled and nonplussed.

What's another word for dumbfound?

Some common synonyms of dumbfound are bewilder, confound, distract, nonplus, perplex, and puzzle.