"flat hand" is correct and usable in written English.
You can use it to describe a hand placed firmly against something, as in, "He flattened his hand against the wall."
Approach him calmly, again with a flat hand.
A flat hand, palm downward, called for smoothness.
Then maybe South would have doubled because he had such a flat hand.
A sloppy salute, flat hand to eyebrow, is a possibility but would undermine serious military saluting.
Open it so they're not grabbing and show them how to pet the dog with a flat hand".
Inter's Thiago Motta gets sent off for shoving his flat hand into the face of Sergio Busquets.
The whole thing writhes with biang biang noodles – flat, hand-pulled and hand-torn, and named for the noise they make when slapped against an oiled kitchen surface, blissfully stretchy and chewy.
Oh good, I'd thought the advent of "Whoop De Doo" had spelled the end of all Cody Critcheloe's weirdly flat, hand-drawn looking videos.
A crab goes by, sideways, flat hands shushing the flashlight's clang.
It was not differentiated whether a participant touched the floor with the finger tips or with flat hands.
Clinical practice guidelines encourage wheelchair users to use handgrips instead of flat hands or fists when performing transfers [ 11].
