I’ve just finished level 42 today and 4 new vocab with the kanji for lawn.
Even with their respective context sentence, I can’t differentiate their nuances.
Since the also have the exact same meaning, this makes kaniwani pure guess work. Same goes with 軸、中軸、枢軸、中枢 too but their nuances a slightly more clear
For this sort of “what’s the subtle difference between vocab” questions, Google Image Search can often help quite a bit. 芝草 generally gets me close-up images of the grass itself, while 芝生 tends to show the lawn as a whole.
Like the Leebo said, though, you’re not confused about the difference with 東芝, are you?