I think I remember seeing the term GPU used in a Byte article from the 80s? It was a while ago when I saw it (~15 years), so I can't really remember any details.
https://archive.org/details/byte-magazine-1985-02/1985_02_BY...
> Two years later, Nvidia introduced the GPU. He [Curtis Priem] recalls that
> Dan Vivoli, Nvidia's marketing person, came up with the term GPU, for
> graphics processing. "I thought that was very arrogant of him because how
> dare this little company take on Intel, which had the CPU," he said.