Looking at old PC keyboards, from IBM Model M to old Gateway 2000 keyboards from the 90's etc, it's looks like it's always been Enter.

But terminals and UNIX machines were more likely to use "Return", e.g. looking at a DEC VT100 or Sun SPARCstation keyboard.

edit: looks like most of the 8-bit machines like Commodore, Atari also used Return. So Enter was mostly an IBM thing.