used in some expressions <as, like> negro spirituals

Hi,

I wrote "negro is still used in some expressions asnegro spirituals". Someone corrected it to "negro is still used in some expressions like negro spirituals".

I thought that as and like where exact synonyms, and that using one or the other was just a question of personal preference. Could someone explain me what makes a difference?

Please help.

Thanks!

I didn't find the right solution from the Internet.

References:
forum.worfbhcgreference.com/threads/used-in-some-expressions-as-like-negro-spirituals.499166/
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