Exergue. It's pronounced EXerg.
Now, is this black hole of a word something that, well, used to be an...er...erg?
Nope. It's something you see more or less every day. Something you often hold in your hand.
Something you're pleased to receive, but quite resigned to giving to complete strangers.
Do you know what it is, yet?
An exergue (it really is a horrid word) is the bit of the reverse of a coin or medal underneath the main design. It quite often has the date in it.
As it happens, most of our newest and really elegantly beautiful British coins, (designed by Matt Dent) don't have an exergue, but our fifty pence coin (seen at the bottom of the illustration below) does.
Actually, though, I rather wish that was something I didn't know.
Sunday Rest: exergue. This word came to us from French, and before that from the mediaeval Latin exergum, from the Greek ex, outside, and ergon, work. Interestingly, the French for outside the work is also used in English: hors d'oeuvres.
I could probably make some joke about this, but don't quite dare.