motionlessly; stock-still; quietly
Describes a state of being completely still, often from shock, awe, or intense focus. Literary and somewhat formal.
その知らせを聞いて、彼は凝然として立ち尽くした。
Upon hearing the news, he stood stock-still.
観客は凝然として舞台を見つめていた。
The audience watched the stage without the slightest movement.
凝然 is a compound of 凝 (to freeze, congeal) and 然 (state, like that), combined with the quotative と and して to form an adverbial phrase. The exact historical derivation is uncertain, but the expression has been used in classical and literary Japanese to describe a frozen, motionless state.