I just looked up "oceanic," and the definition distinguished oceanic waters from "littoral or neritic waters."
I had a vague idea that "littoral" was something to do with margins, and indeed it turns out to describe things on or near the shore. But I don't think I had encountered "neritic" before; it refers to shallow coastal waters.
Apparently "neritic" may derive from "Nerita," a genus of marine snails. Huh.
While I'm here, I may as well note that "pelagic" means the same as "oceanic" in this context, whereas "bathypelagic" refers to the deeper ocean waters. It's not clear to me whether "abyssal" is a synonym for "bathypelagic" or a step deeper yet.
Littoral, neritic, pelagic, abyssal. An impressive series of words. Any suggestions for other impressive series?