"Cassette" is just appending the French dimunitive "ette" to "casse", which means "case". So "cassette" just refers to something being in a little box. The word itself has nothing to do with there being tape inside.
In English, the word became strongly associated with cassette tapes because it wasn't widely used before those came around, but the word itself is much older and more general.
In English, the word became strongly associated with cassette tapes because it wasn't widely used before those came around, but the word itself is much older and more general.