Comment by schoen
7 hours ago
Wiktionary's note says some people think this root may originally have referred to freshwater/inland seas, not oceans.
https://en.wiktionary.org/wiki/Reconstruction:Proto-Indo-Eur...
In many of the daughter languages it does regularly include saltwater connected to the world ocean (certainly the Latin "Mare Nostrum" for the Mediterranean!); it just seems uncertain from this description whether it necessarily had that sense in PIE.
That doesn't seem like "had no ... word for ... 'sea'" is a very clear or helpful description of the situation, though.
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.
After growing up for decades in Michigan and seeing the surrounding Great Lakes regularly, the oceans were a bit disappointing. Besides the salt. I knew it was salty but I wasn't expecting pickle juice.
There was one major distinction, which was "is it drinkable?" Someone crossing the North American Great Lakes (before pollution), didn't need to store water. But they would crossing an ocean, or the Caspian Sea. It's not like you can use seawater to irrigate most crops (except seaweed and a handful of others).
"Mere" in English doesn't seem to refer to saltwater at all. Nearly always small lakes and mostly in certain locales of eastern England.