Antonyms:
* Bore: To make someone feel tired and impatient.
* Disappoint: To fail to fulfill someone's hopes or expectations.
* Displease: To cause someone to be unhappy or angry.
* Unimpress: To fail to make someone feel admiration or respect.
Synonyms:
* Amazed: Filled with wonder and surprise.
* Astonished: Filled with great surprise or wonder.
* Bewildered: Confused and disoriented.
* Dumbfounded: So surprised that one is unable to speak.
* Overwhelmed: Filled with such strong emotion that one is unable to cope.
* Startled: Suddenly surprised.
* Stunned: Shocked and dazed.
* Surprised: Feeling or showing sudden wonder or alarm.
The best antonym or synonym for "astound" will depend on the specific context in which you are using the word.