I’m not sure I am being clear.
Some meanings are so close to each other and yet, différents words are used for the meaning.
Why is that ?
Is that because the Japanese terms are so precise that it has only this meaning, and all other synonymous are not correct, or (but I can’t imagine that) maybe Wanikani haven’t noticed them ?
Therefore I use the synonym fonction to add the same meaning to close words, but I was just wondering about the reason.
Unfortunately you’re not going to find any answers asking the users of the forum. The Wanikani team do what they do, they don’t usually explain why. Their stated goal is to teach you kanji, and they include vocab to reinforce what they consider the most useful the kanji readings. You’ll have to ask them directly if you want to know how or why they did something.
@Leebo’s post above was intended to elicit a specific example set of words you were struggling with from you, so we could hopefully highlight some of the subtleties in meaning.
For example, 上る, 登る and 昇る are all read のぼる, and mean “to climb”, but their usages are different. 上る = small things like stairs or ladders, 登る = big things like mountains, 昇る = the sun climbing into the sky.