Originally Posted by ImaginaryIllusion
Polygamy involves conjugal unions, ie: it's a form of Marriage.
Polyamory is about relationships...romantic, and generally intimate. But as any long married person could tell you, romance and marriage don't necessarily have anything to do with each other.
But since marriage to more than one person isn't allowed in most western cultures, I think using that term for marriage-like relationships as well makes a lot of sense. After all, even what's commonly thought of as polygamy isn't legal polygamy.