A person or thing that astonishes or amazes; something that causes great surprise or wonder.
From 'astonish' + '-er' (one who does something). A straightforward agent noun formation, though rarely used compared to 'wonder' or 'marvel.'
An 'astonisher' isn't a common word, but when someone pulls off an incredible magic trick or surprise, calling them an 'astonisher' sounds way cooler than just saying they're amazing.
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