The answer is geas. In Irish, it is an idiosyncratic taboo, whether of responsibility or prohibition, similar to being under a vow. The plural is also used to mean exactly a spell prohibiting some action, common in Irish folklore and legends. It can be associated with a curse or, ironically, a gift. If someone under a geas break the associated taboo, the infractor will grieve dishonor or even death. On the other hand, the observing of one's geas is thought to bring power. Frequently it is women who place geasa upon men. In some cases the woman turns out to be a goddess or other sovereignty figure.
