I believe there never was anybody with such an imperturbable countenance when she chose.
All the rest of that day, and from morning to night afterwards, she sat at that desk, scratching composedly with a hard pen, speaking in the same imperturbable whisper to everybody; never relaxing a muscle of her face, or softening a tone of her voice, or appearing with an atom of her dress astray.
There are no more uses of "imperturbable" in the book.
Show samples from other sources
Silas was imperturbable.
Neil Gaiman -- The Graveyard Book
Out of loudspeakers all around Zollverein, the staccato voice of the Reich grows like some imperturbable tree; its subjects lean toward its branches as if toward the lips of God.