The phrase "a hard expression" is correct and usable in written English.
It can be used to describe a phrase or statement that is difficult to understand or interpret.
Example: "The poem contained a hard expression that left many readers puzzled about its true meaning."
Alternatives: "a complex phrase" or "a challenging statement".
Wearing a steel-grey suit and a hard expression, he nodded as the curator made her case for the works of Andrei Busel, a street artist.
He had a sharp, lean face, with tufts of hair on his chin and above his lip, and a hard expression that could be mistaken for actionable annoyance; you got the feeling that he might suddenly pull a ball-peen hammer from beneath his blanket and bop someone on the head, but, of course, he was not likely to do any such thing.
He took his position at the oars, then waited with a hard expression while Milo and his mother climbed in under the canopy.
As two diagnostics companies learned recently at their expense, the FDA is taking a hard look at gene and protein expression based tests.
In the coming months, I'd see some of them walking around with dried blood on their uniforms and a hard, tight expression on their faces.
As you drive from the east to the west side of Aleppo, past billboards of Assad and Putin wearing hard expressions, the universal destruction turns into a bustling, intact city.
With her tentative movements, scrappy bangs and hard expressions, she gives us both striver and na? a woman blind to how much she yearns for until she lands in a Manhattan of fur-trimmed coats.
A smile is the hardest expression to fathom.
Do you have a hard time controlling facial expressions?
We also derived the theoretical closed-form expression for a hard decision demodulator with no-memory signaling.
"I choose to tell them when I get the feeling that they are having a hard time understanding my different expression of anxiety," she added.
