The words "fiancé" and "fiancée" exactly fit the pattern of the past participles of some French word "fiancer," which would be the "to do that" form of the word. For example, if fiancé and fiancée meant "gone," then then fiancer would mean "to go." I was wondering in the shower what fiancer would mean if it were really a French word, with my top choice being "to bind or tie." Something like "to dedicate" would also be cute. So, I looked it up.
It is a real word—it means "to be engaged." So, fiancé and fiancée mean "been engaged." Sigh. How anticlimactic.