Cox made them down to .010 size. I only had the .049 ones- the literature I read back then (1971-1974ish) called them hot-head diesels.
“Hybrid” seems to be used a lot, and I’m not aware it’s used much for people, or seen as offensive by anybody. “A cross between”, perhaps? Phrases with “quasi” in them? “Blend of” and the like?
I think Quasi- would work in this case as there are precedents already:
I present the Quasiturbine!
https://www.mh-aerotools.de/airfoils/cox_teedees.htm
Those little Tee Dee .01 engines were pretty cool. Now they’re worth hundreds of dollars. I think I had somethjng with a .010 in it, but I definitely had a plane with a .020, and several with an .049. And a Corsair with a big K&B .61 in it, and another plane with a .40. Now everything is electric, and while I admit those little engines were cool, I do not miss futzing around with nitro, fighting to get them started, and cleaning all the reidual oil off everything afterwards.
I do think they count as diesels, since they rely on compression to fire, and not an external spark with timing.
Quasi-diesels? Yeah, loved the .049 line control models. My buddy had a Stuka that looked really good, it even had the dive whistles. We also tried converting one for free flight, although it ended pretty spectacularly. I’ll post a story about it when I have time.