Gessi

In Irish, a geas (alternatives: geis, géis, deas; plural geasa) is an idiosyncratic taboo, whether of obligation or prohibition, similar to being under a vow. The plural is also used to mean specifically a spell prohibiting some action, common in Irish folklore and mythology. It is this additional meaning of the plural which the article discusses.

The equivalent Scottish Gaelic word, also used in English, is "geas" ([ˈkes], plural "geasan").

A geas can be compared with a curse or, paradoxically, a gift. If someone under a geas violates the associated taboo, the infractor will suffer dishonor or even death. On the other hand, the observing of one's geas is believed to bring power. Often it is women who place geasa upon men. In some cases the woman turns out to be a goddess or other sovereignty figure.

The geas is often a key device in hero tales, such as that of Cúchulainn in Irish mythology. Traditionally, the doom of heroes comes about due to their violation of their geas, either by accident, or by having multiple geasa and then being placed in a position where they have no option but to violate one geas in order to maintain another. For instance, Cúchulainn has a geas to never eat dog meat, and he is also bound by a geas to eat any food offered to him by a woman. When a hag offers him dog meat, he has no way to emerge from the situation unscathed; this leads to his death.

A beneficial geas might involve a prophecy that a person would die in a particular way; the particulars of their death in the vision might be so bizarre that the person could then avoid their fate for many years.

There is a considerable similarity between the Goidelic geasa and the Brythonic tynged. This is not surprising given the close origins of many of the variants of Celtic mythology.

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