Synonyms for Astound:

n.

shake up, spring a surprise, flash mob, stagger. awe. astound (noun)
overwhelm, astonish, shock, bewilder, stun, startle, amaze, surprise.

v.

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

Other synonyms:

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

Usage examples for astound

  1. I can foresee what he will do, but you will astound me yet. – Fables for Children, Stories for Children, Natural Science Stories, Popular Education, Decembrists, Moral Tales by Leo Tolstoy