Gerund noun meaning the act or process of bewildering or astonishing.
Definitions
The act or process of causing astonishment or great surprise; bewilderment. His dumbfounding of the audience left them silent for minutes.
dumbfoundgerund / present participle Used attributively in its present-participle form 'dumbfounding'
Definitions
Causing great astonishment or bewilderment; astonishing. The team achieved a dumbfounding victory against the champions.