What is the fullform of rip?

Answer 1

"Requiescat in pace". This is a Latin phrase that translates to "rest in peace", which also can be shortened to RIP, so either fits. But originally the Latin term is what was used, Latin being considered a weightier language and more befitting as an epitaph.

Note that both instances of the letter C would have been pronounced like a K, making it "reh-quee-eh-skat een pah-keh".

Answer 2

Rest in pease.