Mithril is an apocryphal metal invented by J. R. R. Tolkien, which goggle-eyed little hobbits hide under in Lord of the Rings. It supposedly of Elvish origin. Resembling silver but being stronger and lighter than steel — so light, allegedly, the user doesn’t feel its weight — it is very adaptable and can easily be forged into a McGuffin. For example, if you thow it over yourself when the Nazgûl ride by they won’t see you because you will look exactly like a rock.[1]
Contrary to popular belief, client money is not made of mithril. Nor are legal opinions. For absolute certain, none of the views expressed on this site are either. Yes, that’s another disclaimer, by the way.