Learn That Word

Synonyms for Stupefying (same or very similar meaning)

WordNet sense 1 (causing loss of physical or intellectual bearings):
disorienting

WordNet sense 2 (so surprisingly impressive as to stun or overwhelm):
astonishing, astounding, staggering

WordNet sense 3 (making a strong or vivid impression):
impressive

WordNet sense 4 (causing alarm or fear):
alarming


From the ODE community, based on WordNetadd/edit