What's a posnet?

This is a cast iron posnet. I asked the same question you're asking: What's a posnet?

The term was coined in 1327 England, to mean a "small pot".

Also called "sauce pots" or "butter pots", they're meant for melting butter or making sauce.

They were also used in the Revolutionary War to melt lead for musketballs.

I've never seen one with a wire handle, so I don't think they were hung over a fire; They could be used over coals or on a wood stove.

Lodge used to make a similar pot, and called it a "water skillet". I guess that means it's a skillet for boiling water?