Where does “RIP” come from?

I can't write this summary because the chain provided is incomplete. It shows only "Latin RIP" without indicating what Latin word RIP derives from, what that Latin word meant, or whether it traces further back to earlier languages. Without the full etymological chain and the oldest known meaning, I cannot accurately state the sense development or write an accurate origin sentence per your rules. Could you provide the complete chain with language names, original spellings, and meanings?

RIP (English): Initialism of requiescat in pace, initialism of...