The word disc can describe any round, flat object. The word disk can also describe any round, flat object. So what exactly are the rules that dictate when we choose disc over disk, and vice versa?
There’s no tidy etymological backstory behind the distinction between the two terms: Disk and disc both come from the Latin discus (in Greek, diskos). The oldest known references to the English version, dating back to the mid-17th century, are spelled disk. The American Heritage Dictionary of the English Language (per Grammarphobia) chalks this up to the precedent set by similar -isk words already in the lexicon, such as whisk. But by the following century, some English speakers influenced by the term’s Latin predecessor had started opting for disc, instead.
For the next couple hundred years, the only thing that might determine with any consistency whether you wrote disc or disk was where you lived: Americans favored disk, while disc was the spelling of choice in the UK. But even that wasn’t a hard and fast rule; and as Merriam-Webster points out, both spellings occasionally appeared in a single text, as was the case in Jones Quain’s 1828 book Elements of Anatomy, Vol. 1.
It’s still a toss-up between disc and disk for many kinds of discs (or disks). Herniated ones, for example: It’s herniated disk to the Mayo Clinic, but herniated disc to the American Association of Neurological Surgeons. In certain cases, though, one spelling is so much more common that you could go so far as to consider the other one wrong. The music industry has used disc more frequently than disk ever since disc-shaped records became popular in the late 19th century, and modern music-related phrases like compact disc and disc jockey generally stick to that rule. In tech, however, engineers named magnetic computer disks floppy disks, and the k has stuck for those square disks and the disk drive where they’re inserted (even if today’s kids have never actually seen that process in action). And if you’re describing a Frisbee, go with flying disc—not disk.
Because there’s no clear logic to explain these conventions—each was pretty much just a spelling trend that caught on—it’s hard to remember which things are discs and which are disks. But Merriam-Webster does have a handy trick to help: Compact discs (and flying discs) are round, just like the letter c. Floppy disks are all lines and edges, just like k.
Have you got a Big Question you’d like us to answer? If so, let us know by emailing us at firstname.lastname@example.org.