This article is about the taboo in Irish mythology. For the band, see Geasa (band). A geis can be compared with a curse or, paradoxically, a gift. If someone under a geis violates the associated taboo, the infractor will suffer dishonor or even death.
In Irish mythology and folklore, a geis (/ˈɡɛʃ/; [ˈɟɛʃ]; plural geasa) is an idiosyncratic taboo, whether of obligation or prohibition, similar to being under a vow or spell. The Scottish Gaelic spelling "geas" is also common.