When is an album not an album? Why, when it’s a “non-fungible token”, a new form of digital swag, related to cryptocurrency, being sold by artists and musicians such as Kings of Leon and Grimes. They’re called NFTs for short, but why?

Perhaps disappointingly, “fungible” does not mean “capable of being turned into fungi”. Rather, the Latin verb fungi means to discharge some office or perform some task, and so fungibilis means “useful”, and English “fungible” specifically describes useful things that are interchangeable. If I order five spoons of a certain design, it doesn’t matter exactly which five of those spoons you send me.

The OED says the word was first used in English by the diplomat Anthony Ascham in 1649, though the citation it gives is actually, according to Early English Books Online, from a 1676 treatise on maritime law, De Jure Maritimo et Navali, by Charles Molloy and Robert White. Of money, they write: “Take away this fungible Instrument from the service of our necessities, and how shall we exercise our Charity?” Money is the paradigmatically fungible good, since one £10 note is as good as any other. Writers, though, are definitely not fungible.

• Steven Poole’s A Word for Every Day of the Year is published by Quercus.