Here’s the quick story behind this word, just because it sounds so cool: zelotypia is another word for jealousy.
Introduced into English via Latin in sixteenth century, zelotypia has its roots in Ancient Greek and represents pretty much a direct transliteration of the Greek word for jealousy, zelotupia. In the sense of a hotly-felt emotion, it derives from the same root as the likes of zeal, zealot and zealous, as well as jealous; all derive from a Greek word, zelos, which could be used to mean “ardour,” “strength of passion,” as well as “envy,” and “keen rivalry.”
Although zelos tended more often than not to have positive connotations in Greek, those negative connotations (“envy”, “rivalry”) can’t be ignored—and, as it happens, ended up informing the difference we see between jealousness and zealousness in English today. So while the positive side of the Greek word zelos developed into our zealous, the negative side of the word (albeit furnished with a new initial letter, thanks to some etymological jiggery-pokery between Latin and French) morphed into our word jealous.
But if zelotypia means “jealousy”, why has English made room for two words meaning the same thing?
Well, it might not look like it, but there is something of a difference here. When it first appeared in the language in the 1550s, zelotypia was actually used as if it were a name, a personification of jealousy and jealous feeling. That somewhat grand sense of the word survived for a time, so that while the word jealous came to be used in a general sense of any feeling of enviousness or covetousness, no matter how serious, its would-be synonym zelotypia remained somewhat weightier.
Over time, zelotypia came to refer to what the Oxford English Dictionary identifies as “obsessive or excessive jealousy,” sometimes serious enough even to be “characterized as an illness.” Indeed, in the handful of dictionaries that list zelotypia as an entry today, it tends to be flagged as a term all but exclusively used in psychiatric contexts to refer to a debilitating, excessive, morbid jealousy.