[simmons]

I don't think it was ever common, since earphones weren't that popular until people started calling them "earbuds", but the term was historically used in at least some circles in the U.S. The 1988 Radio Shack catalog [1] seems to mention "earphone" 57 times, including two mono earphone products.

[1] https://www.worldradiohistory.com/Archive-Catalogs/Radio-Sha...

[slg]

That’s interesting, although that seems to be a different usage than OP mentioned. It seems to be used interchangeably with headphones as it’s also being used to describe cables and jacks.