Here's one I can weigh in on. I realise they have different meanings now, but they didn't always. As language evolves, often words that used to be synonyms are differentiated so that their meanings, while still similar, have a different nuance. An example off the top of my head: sin and crime. Sin was the Old English word for crime, before the Romance word 'crime' entered English, presumably after William the Conqueror invaded and French became the language of court. 'Sin' didn't disappear, it just became a more specialised form of the now general word 'crime' - meaning a crime against God, used to describe moral failings rather than acts hurting others like theft or murder. We still have both words today, and both are useful, even though they originally meant the same. Since the distinction between 'envy' and 'jealousy' is arguably pretty nuanced, I suspect the same thing happened here - both were comparative and related to the difference between what you have and what your neighbour has, I think the differentiation is relatively recent. I'm not sure if this explanation helps you resolve this hill to die on, please let me know if I can elaborate further.