Question about the etymology of "mercury"

Why is the planet mercury named after a metal?!

The metal is named after the planet. Rather, the metal is named after the god. Mercury was the swift-moving winged messenger of the Roman pantheon. The metal mercury is also swift moving. It's very viscous and flows easily, so it works well in thermometers and stuff.

The planet is not named after the metal. It's named after the god.

I agree that the metal is named after the planet (that is in turn named after the god).

In the Middle Ages and Rennaissance, the metals were tightly connected to planets. The astrological glyphs for the planets were routinely used as glyphs/names of the metals. (By astrologers, alchemists, and early chemists.)

But then there were the commonplace English names for metals, too, that we use today (iron, copper, etc). The common name for mercury was "quicksilver," but maybe "mercury" became the standard name to save confusion with silver?