The name “retpoline” is a portmanteau of “return” and “trampoline.” It is a trampoline construct constructed using return operations which also figuratively ensures that any associated speculative execution will “bounce” endlessly.
(If it brings you any amusement: imagine speculative execution as an overly energetic 7-year old that we must now build a warehouse of trampolines around.) [1]
I actually know that word in the compiler meaning, I think I just never got the connection, because I was pronouncing it in my head as ret-poh-line, not ret-poh-leen.