be suddenly unable to speak (because of shock, fear, etc.): We were struck dumb at the sight of three armed soldiers in the kitchen. ♢ The witnesses were struck dumb with terror. ▶ ˈdumbstruck adj.: When I found out that I had won first prize, I was dumbstruck.
As I wrote the words the poor across the board, I faced my students and was struck dumb with a triple realization: that some of them live below the "poverty line"; that no clear definition exists for the words the poor; and that, if I began to pretend that there were, I would be teaching a lie.