What is an adjective for dumbfound?

There isn't a single perfect adjective for "dumbfound," as it describes a state of being, not a quality. However, you could use several words to convey similar meanings, depending on the specific context:

For the feeling of being stunned:

* Astonished

* Bewildered

* Dumbstruck

* Floored

* Speechless

* Startled

* Surprised

For the effect of something being overwhelming:

* Astounding

* Awe-inspiring

* Impressive

* Mind-blowing

* Staggering

For the effect of something being confusing or incomprehensible:

* Baffling

* Mystifying

* Perplexing

* Puzzling

Ultimately, the best adjective to use will depend on the specific situation and the tone you want to convey.