Definition of stun verb from the Oxford Advanced Learner's Dictionary

stun

verb
stʌn
 
; stʌn
 
stunning, stunned
 
1 stun somebody/something to make a person or an animal unconscious for a short time, especially by hitting them on the head
Synonym
knock out
The fall stunned me for a moment.The animals are stunned before slaughter.
2 stun somebody to surprise or shock somebody so much that they cannot think clearly or speak
Synonym
astound
Her words stunned me—I had no idea she felt that way.
3 stun somebody to impress somebody very much
Synonym
amaze
They were stunned by the view from the summit.
stunned
 
;
 
adjectiveShe was too stunned to speak.There was a stunned silence when I told them the news.
Usage noteUsage note: surprisestartle amaze stun astonish take somebody aback astoundThese words all mean to make somebody feel surprised.surprise to give somebody the feeling that you get when something happens that you do not expect or do not understand, or something that you do expect does not happen; to make somebody feel surprised:The outcome didn't surprise me at all.startle to surprise somebody suddenly in a way that slightly shocks or frightens them:Sorry, I didn't mean to startle you. The explosion startled the horse.amaze to surprise somebody very much:Just the huge size of the place amazed her.stun (rather informal) (often in newspapers) to surprise or shock somebody so much that they cannot think clearly or speakastonish to surprise somebody very much:The news astonished everyone.amaze or astonish?These two words have the same meaning and in most cases you can use either. If you are talking about something that both surprises you and makes you feel ashamed, use astonish:He was astonished by his own stupidity.take somebody aback [usually passive] (especially of something negative) to surprise or shock somebody:We were rather taken aback by her hostile reaction.astound to surprise or shock somebody very much:His arrogance astounded her.It surprises somebody/startles somebody/amazes somebody/stuns somebody/astonishes somebody/takes somebody aback/astounds somebodyto surprise/startle/amaze/stun/astonish/astound somebody that…to surprise/amaze somebody what/how…to surprise/startle/amaze/stun/astonish/astound somebody to know/find/learn/see/hear…to be surprised/startled/stunned into (doing) something