I think he meant it as an absurdist joke, but this is a great response!

I looked it up, "gress" comes from "gradi" in Latin which directly translates to "walk". More specifically: con(pro) + gradi -> congredi (verb) -> congressus (noun)

Edit: Knowing this, "gradient" has an interesting flavour :)

Edit: It looks like the path is more indirect for "gradient"

"gradi" (walk) -> "gradus" (step) -> "grade" (french influence) + "salient" -> "gradient". I like that in Latin "walk" is "to step", or perhaps "step" is "the unit of walking"? "A walking"? Etymology is fun!