What is the synonym for astounding?

There are many synonyms for "astounding," depending on the specific nuance you want to convey. Here are some options:

Formal:

* Amazing

* Impressive

* Extraordinary

* Remarkable

* Phenomenal

* Exceptional

* Stunning

* Breathtaking

* Spectacular

* Magnificent

Informal:

* Awesome

* Incredible

* Unbelievable

* Mind-blowing

* Out of this world

* Shocking

* Stunning

More specific:

* Astute (for something clever or insightful)

* Staggering (for something overwhelming in scale or quantity)

* Startling (for something unexpected or surprising)

* Overwhelming (for something that fills you with emotion)

The best synonym will depend on the context of your sentence.