There's nothing wrong with "sublight". In fact, different ships may have different propulsion systems for sublight speeds, so "sublight engines" is probably a good generic term if you're not making a specific engineering reference. BSG muddies the waters a little bit with "FTL", because they use the term of jump drives rather than as a generic category, but I suppose you could use it generically if you wanted to. I'll probably end up using "FTL" as a general category of technologies that allow you to go from one place to another faster than light, but not any specific technology. I'll have separate terms for drive systems that operate on radically different principles (e.g. jump versus warp versus hyperspace).
IIRC, there's a whole debate that underwent on the Star Trek sets about FTL and STL drives and what to call them. I believe the story is told in The Making of Star Trek, but it's been decades since I last read that book.
I've been rewatching old episodes of Dark Matter, and they're using "FTL", "Sublight" and "Blink Drive". As I'm considering similar technologies, I may just follow suit. Perhaps the BSG thing just isn't that big a deal.