The word warm comes from the Middle English word werm, which comes from the Old English word wearm, which comes from the Proto-Germanic warmaz, with still the same meaning. Some think that warmaz is from the Proto-Indo-European root ghwer, meaning "heat", but that's unconfirmed. None of this is surprising; in fact, it's one of the most prosaic etymologies I've ever encountered. It's the word lukewarm which is interesting: what does luke mean? How did the 29th most common name in the US get in front of a noun? Well, it has nothing to do with the name; it's an old word also meaning "warm"! The compound was made in Middle English, when luke was already archaic. This is from Old English hleow, which had an additional definition of "sunny". Through Proto-Germanic khlewaz, this is said to trace to the Proto-Indo-European root kele, still meaning "warm". So, yeah. Warm-warm.
Adam Aleksic, a rising sophomore studying linguistics and government at Harvard University, has been described as the internet's sixth most famous etymologist. He also has disturbing interests in politics, vexillology, geography, board games, conlanging, and law.