expression, i-adjective
at a loss for words; speechless; dumbfounded
Used when someone is so surprised, shocked, or overwhelmed that they cannot say anything further. Often follows a statement or question that leaves the person unable to respond.
あまりの光景に、二の句が継げなかった。
I was so stunned by the sight that I couldn't say another word.
彼
She seemed at a loss for words at his sudden confession.