I found myself in a quandary some time ago. How could I refer to a fat person in a clinical manner without using more than a single word? We obviously already have terms like fatty and gargantua, but those carry a negative connotation. I wanted something neutral.
Since obese comes from the French obésité, I thought it fitting to tack on the -eur suffix, giving us obesiteur. Now, the problem is that in French, this is a masculine ending. If we want a corresponding feminine ending, we'd get obesitress, or in the French spelling, obesitrice. I'm not sure how much I like gendering nouns in English, so I'd probably relegate my usage to the male-only.
As you've guessed, the French comes from Latin (obesitas), so another valid construction would be using the Latin agent suffixes -or and -rix, giving us obesitor and obesitrix. I will admit, I cackled for a good thirty seconds after "obesitrix" came into my mind. I could only think of things like, "He bowed genuflect to truckle and beg, but her ears were shut and her mouth open. Eyes wide like a horse in terror, he swiftly fell into the maw of the obesitrix." I blame it on the BDSM community.
If we're dipping into the crass, I can likely think of many more words, obeast being chief among them, but let us forbear. What else might ring neutral enough? Paunch-bearer? The hyphenation feels like cheating. I get a chuckle out of obeseling due to its oxymoronic nature. Sebacle (sebaceous debacle)? Oh no, we've veered once more into the pejorative... I would probably also run amiss by suggesting impressionist, one who leaves impressions (as they walk). My better judgment would prevent me from suggesting chairbane and expandrake (the ever-increasing dragon).
It might also be fun to come up with a term for a skinny person. Spareling, skeleton, leaniac, exhiribtionist (one who exhibits their ribs), svelton. I do like svelton, but that comes with a connotation of elegance that isn't endemic to all skinny people.
