[iamcurious]

Interesting, that definition of "prequel" creates a strange conceptual symmetry with the word "sequel".

Both "prequel of A" and "sequel of A" imply "published later than A but set in the same universe", with "pre" and "se(q)" referring to the timelines, we can factor out "quel" to mean just that. I guess "Back to the future III" would be neither a sequel not a prequel, but definitely a quel.