From Longman Dictionary of Contemporary Englishbe struck dumbbe struck dumbSAY#to suddenly be unable to talk, usually because you are very surprised or shocked → dumbstruck → strike
Examples from the Corpus
be struck dumb• I was told it was Duart was struck dumb.• One edged remark, and she would be struck dumb.• At times 25,000-plus onlookers were struck dumb by tension and anticipation, a hiccup resounding like a roar.• Once again I was struck dumb by the mystery of the world.• No wonder the computer wizards were struck dumb by the place; the narcissistic attraction must have been overwhelming.• Amy was struck dumb. Was it possible that her own son had deceived her?• When he arrived at the scene of the disaster, he was struck dumb with horror and amazement. 