Yep, it's the same in Māori, a Polynesian language, where "moana" refers to oceans and large lakes alike.

What's really interesting is that in Hawaiian, a close relative with some sound shifts (k/t, l/r, n/ng, so taboo is kapu in Hawaiian, in Māori, tapu, path is ala / ara, the God of the sea is Kanaloa/Tangaroa) they have more than one word for ocean, kai is coastal waters, moana is the deep ocean.

But it makes sense in the geographical context of both societies and how they evolved to their environment, the Hawaiian archipelago is made up of multiple smaller islands separated by waters exposed to the full force of the Pacific, while the archipelago of New Zealand is dominated by two large landmasses separated by a narrow strait that together are about the same area as Germany.

So the Hawaiians remained more tightly wedded to the sea to build their archipelagan societies than the Māori did.

In fact, the Māori lost the knowledge to build ocean-going vessels like the ones that had carried them to New Zealand within a few hundred years because there was no need for it. And their language lost the distinction between "coastal waters" and "ocean" while Hawaiian retained them.

While we have evidence of Māori traveling to Raoul in the Kermadecs early on, as classical Māori culture evolved on much much larger islands, their technology focus on boats switched from ocean going vessels to coastal travel and river travel.

In fact, while "Wai", water, is often considered the Māori word for "river", there's another word that also means river in Māori:

"Ara" - path.

(Of course, it still means a regular path)

You can see the same with the word "sea". Its German equivalent See still mainly means "lake", even though in some fixed expressions it can be translated as "sea" (e.g. Nordsee, Ostsee).

It is probably not a substrate word, but more likely coming from "dead" water, as in not a moving river.

The cognate set is real, but jumping from that to "PIE had a word for the sea" assumes the original meaning was already maritime

That doesn't mean no word for sea. It means sea refers to any large body of water that you dnn't see the other side of, like in some (all?) other language families. There is no discernible distinction from the perspective of the ancient observer. The Great Lakes look like oceans. Saltiness isn't of great relevance since there are salt lakes, too.

Finnish language doesn't have an actual word for "ocean". We use "valtameri", which means something like main sea or great sea. And both "valta" and "meri" are Indo-European loans.

But in Livonian (an almost extinct Finnic language spoken in Latvia), Valdamer is one of the names for the Baltic Sea. So maybe that's the origin of the Finnish term as well.

> (I actually remember asking the professor why they had a word for "ocean", but he wasn't sure either.)

Most likely a reference to Houses of the Holy.