Yep, "piedfort" are double-thickness coins, struck for collectors. The glossary doesn't tell you how to pronounce it. It's a French loanword and usually pronounced in the French fashion, something like "P.A.4" - three syllables, with the "D" and "T" silent.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis