Douglas Harper's Etymology Dictionary
"expressionless, impassive," 1934, American English, of unknown origin.
Usage examples of "po-face".
Queer little thing, with a po-face and fine gentry airs, but awful frightened of her enemies.
The girl who used to live here, last winter… Queer little thing, with a po-face and fine gentry airs, but awful frightened of her enemies.
Well, Sharon was grinning from ear to ear, Magda was smiling demurely and Benjamin was wearing his professional po-face with a hint of cheer.
I don't want to spend thirty years being a glorified commissioned clerk, or marry some po-faced whiskey-swilling mercenary and breed a litter of officerlets.
But it was hard to look po-faced at a kid having fun, especially with a close friend's daughter who'd been in and out of your house all her life.
But it was hard to look po-faced at a kid having fun, especially with a close friend’s daughter who’d been in and out of your house all her life.
But Egremont no longer mattered -- he lived in a different world, now, with his po-faced respectable wife, and his respectable children, and his respectable seat in Parliament.
But Egremont no longer mattered—he lived in a different world, now, with his po-faced respectable wife, and his respectable children, and his respectable seat in Parliament.