When I started sketching out the first pose I didn't get far before I decided to reference them. 2 different photos for 2 poses with slight adjustments. I'm a bit rusty with the dynamics of my people so I think the move helped this one a ton.
The oldest usage of "powered armor" goes back to E.E. "Doc" Smith's Children of the Lens (1947). Smith had already featured "space armor" that was proof against rifle fire and death rays in Triplanetary (1934), but those were not power-driven, just armored spacesuits. I suspect Smith made them motor-driven later because the armor was becoming so thick and heavy no human could move it. XD If we are ever out there exploring the galaxy, I bet that we will be wearing armored space suits rather than anything the characters in Star Trek wore- asides from, well, the harsh environment of space, once doesn't necessarily want to expose yourself to whatever might be floating about in an alien atmosphere.
They did exactly 'coin' it per se(bad wording on my part), but they just bluntly named it "power armor" So I always think of that when it comes to the name. I do somewhat consider "power armor" to be reserved for heavier armors, but a powered suit would generally be a bit bulkier that most normal suits; really anything that enhances your capabilities I suppose.