Used attributively in its past-participle form 'dumbfounded'
Translations
She stared with a dumbfounded expression when she saw the bill.
Elle avait un air stupéfait lorsqu'elle a vu l'addition.
sidéréPlus soutenu; possible dans un registre soigné. Being in a state of astonishment or bewilderment; rendered speechless by surprise. She stared with a dumbfounded expression when she saw the bill.