"impassive" in the adjective sense
1. impassive, stolid
having or revealing little emotion or sensibility not easily aroused or excited
"her impassive remoteness"
"he remained impassive, showing neither interest in nor concern for our plight"- Nordhoff & Hall
"a silent stolid creature who took it all as a matter of course"-Virginia Woolf
"her face showed nothing but stolid indifference"
2. deadpan, expressionless, impassive, poker-faced, unexpressive
deliberately impassive in manner
"deadpan humor"
"his face remained expressionless as the verdict was read"
Source: WordNet® (An amazing lexical database of English)
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