The Impassive Footman was created in 1932.

a

Well impassive means having, or revealing, no emotion; Still or motionless.

So impassive expression should mean that the person isn't showing much emotion

The man's face was impassive; whatever questions we asked, he would give nothing away.

It's impossible to get through to her; she just remains impassive no matter what happens.

The huge rock stands alone in the desert, completely impassive, like a judge pronouncing sentence.

Massive

Passive