Synonyms for Astonish:

n.

shake up, stagger, spring a surprise, flash mob. awe. astonish (noun)
amaze, astound.

v.

amaze (verb)
impress, daze, astound, stun, surprise, overwhelm, dazzle, bewilder, amaze.
surprise (verb)
bewilder, daze, catch unawares, overwhelm, startle, amaze, jolt, stun, stagger, take aback, astound, shock.
wonder (verb)
fascinate, gape, wonder, marvel, stare, engross, gawk.

Other synonyms:

stagger, flash mob. amaze
astound, awe.
surprise
amaze.
Other relevant words:
stagger, awe, spring a surprise, shake up, catch unawares.

Usage examples for astonish

  1. And perhaps I could tell you a thing or two would astonish you more than me, ma'am. – Springhaven A Tale of the Great War by R. D. Blackmore
  2. They astonish and wound me. – The Complete Project Gutenberg Works of George Meredith by George Meredith
  3. Crayford instantly interfered- so vehemently as to astonish all who knew him. – The Frozen Deep by Wilkie Collins