All 3 Uses

impassive
in
The Thief, by Turner
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He remained impassive, but the magus told me that in the future I could ignore conversation that was not directed toward me and I should keep my mouth closed unless specifically addressed.†
Chpt 3 *
She looked beyond me, impassive, distant, not unaware of my presence but unmoved by it.†
Chpt 9
With the sound of water roaring in my ears, I ran for the staircase, past the gods, who watched impassively.†
Chpt 9

impassively = in a manner showing little emotion

Definitions:

(1) (impassive)
having or revealing little emotion -- especially under circumstances others would find exciting
(2) (meaning too rare to warrant focus)