The idiosyncratic taboo or prohibition placed upon heroes and prominent personages in Irish narratives. In certain contexts the imposition of a geis may require a positive demand or injunction or may specify other actions as forbidden or unlawful. In yet other contexts it may be synonymous with the English incantation or spell, and perhaps even a point of honour.
Many of the thousands of instances of an imposed geis initially appear capricious or wilful, until they are seen in a larger context. Cúchulainn, for example, was forbidden to eat the meat of a dog or hound; but he earned his name [Cú, hound; chulainn, of Culann] when he killed a ferocious dog. That so many gessa are imposed upon kings-e.g. that the ruler of Tara should not have the sun rise above him while he was still in bed there-suggests the concept may have originated in early rituals of kingship. Some are prescribed by druids at birth. The breaking of a geis often brings instant death and sometimes also ill favour or destruction to the culprit's people.
Many gessa are imposed by women upon men. In several stories of the Sovereignty figure (usually seen first as a disgusting hag), she defeats the hero in a game or asks him a riddle he cannot answer and rewards herself with a geis he initially finds impossible to perform. In several love stories, e.g. Deirdre, Gráinne, and Diarmait, the heroine places the hero under geis to elope with her. See also GLÁM DÍCENN.
See John R. Reinhard, The Survival of Geis in Medieval Romance (Halle, 1933); Phillip O'Leary, ‘The Honour of Women in Early Irish Literature’, Ériu, 38 (1987), 27–44; ‘Honour-Bound: The Social Context of Early Irish Heroic Geis’, Celtica, 20 (1988), 85–107.