As I am going through my reviews, every now and then I’ll run into one of these:
海岸
沿岸
沿海
臨海
The Japanese reading is no problem, but I cannot nail down the meanings because they all semantically run into each other. They alternate between various very similar meanings like shore, seaside, coast, coastal waters. Honestly, those are all really similar and I don’t understand the difference. Is there a reason that these words don’t all automatically share synonyms? Is there a connotation I should be aware of or can I just go ahead and add “shore” to all of these in the synonym section and call it a day?
海岸 (jpdb frequency ranking: top 7000)
This is most often heard when talking about the shape of the landform as a whole. Like, I can tell people I’m from アメリカの東海岸 (the east coast of the United States). Though it could just mean the coast as a place you visit as well.
沿岸 (jpdb frequency ranking: top 21300)
This is the area along a body of water (more about the land along the water, and less about the place where they meet up), but it’s not limited to 海. A river or lake can have an 沿岸, but it can’t have a 海岸.
沿海 (jpdb frequency ranking: outside top 30000)
This is like 沿岸 but it’s only for 海.
臨海 (jpdb frequency ranking: outside top 30000)
This means “海に臨んでいること” which is more like “looking out over the sea.” You obviously have to be along the sea to look out over it, but you would use this to talk more about structures or things that face the sea than about the general area.
They all differ in terms of nuance/context, in the same way that the four English words you used (shore, seaside, coast, and coastal waters) all differ from each other. Those 4 words are all similar, but each conveys something a little different.
I lived in a small seaside hamlet on the east coast where I spent most of my summers fishing in the coastal waters north of there. Once when my boat sank, I had to swim to shore and barely made it.