I gave you the correct source. The -ic- in ethikos forms an adjective from the noun, just like the Latin form -alis that you see in "morals". There is of course zero semantic distinction between a noun and its own adjectival form.

If you look up "moralis" in Lewis and Short, you'll see a citation noting that the word was coined by Cicero as part of a protest against the idea that Latin was unsuited to the purpose of discussing philosophy (popular opinion at the time being that you had to use Greek for that purpose). It begins by noting that "mores [are what] the Greeks call ethe".

The Greek and Latin words are translations of each other, and both refer to habits and norms. It is true that in modern English norms are a distinct concept from ethics. (Not true in Greek!) But it is not true that in modern English morals and ethics are distinct from each other.