To coat something is to cover it with a thin layer, in order to protect it. I can use a coat of paint to protect metal from rust. Nice and thin, easy to apply, can last quite a while, good stuff paint. I once had a friend who, when he came for supper, would coat his potatoes with butter, like tons of butter. Not sure what was being protected in that case. Was he protecting against the taste of potatoes?
You can put a coat of powder on something using an electrostatic method. Connect the electrodes to the, for instance, filing cabinet, and the sprayed paint all sticks to the cabinet. No overspray or on anything but the metal cabinet. Very clean. I once had some filing cabinets done at our office on the carpet. Amazing. Powder coat is extremely durable and a choice way to paint wheels and car frames etc
When we refer to a coat, that is usually the outermost piece of clothing that can be long enough to cover (if we add a hood or collar) from head to toe. That is the outer coat. We might be wearing a petticoat next to our skin and maybe a dressy waistcoat in between. I might also have put a coat of polish on my nails and coated my lips with gloss. Inside me, my body produces a coating on the inner wall of my stomach
Nature can coat an entire meadow with daisies. It can coat an entire mountain range with snow. It has already coated the polar caps, both north and south, with ice. Nature gives birds a coat of feathers, the deer a coat of leathery skin and fine hair. The hair on a polar bear has hollow centers to provide a coat with greater insulation. Jacob, also called Israel, gave Joseph a coat of many colours
In medieval times the knights wore metal coats of armour. Heavy, awkward and not all that effective, but they had them. There was also a protective shield (cousin to protective coat?) and on that shield was a coat of arms, which was not a coat at all, just an image. That image/coat represented the group that the knight was fighting for. You can find books full of the Coats of Arms of many a family at the library.