Possible noble or priest in c. 6th century Ireland
Life.
Nisi (pronounced "Nishy") was born in 6th century Gaelic Ireland, the son of {{em|Niata}} and brother of Saint Caillín, the patron saint of Fenagh.{{sfn|Ó Donnabháin|1828|pp=181}} He belonged to the tribe of Conmaicne-Rein who lived in present-day South Leitrim and West Longford. He was probably a noble or a priest, and close associate of his sibling Caillín. Little else is known of his life.
His death is described in both prose and rhyme by the ancient {{em|Book of Fenagh}}{{sfn|Monks of Caillín|1300–1350}}{{sfn|Mac Phaidín Uí Mhaoil Chonaire|1516}} along the following lines. Sometime in the 5th or 6th century, Nisi and Caillín journeyed from Ard-Carna Monastery in Roscommon eastwards towards Cora Droma Rúisc crossing the river Shannon to {{em|Magh-Cellachain}} ("the plain of Cellachan"), staying overnight at a place named "the Bennachan",{{sfn|Ó Donnabháin|1828|pp=180}}{{#tag:ref|The {{langx|ga|Bennachan|link=no}} place name is obsolete, but may correspond to present-day {{em|Keenaghan townland}} ({{langx|ga|Caonachán|link=no}}) beside Carrick on Shannon|group=n|name=bennachan}} in the home of "Cellachan", who was not of the Conmaicne tribe.{{sfn|Ó Donnabháin|1828|pp=186}} Next morning for some unknown reason, Nisi was killed unlawfully by Cellachan who then had to pay Nisi's brother a substantial "body fine" and honour price in compensation.{{sfn|Ó Donnabháin|1828|pp=181}}{{sfn|Ó Donnabháin|1828|pp=187}} Nisi was interred at Fenagh.
Legacy.
For the following millennium, the locality where he died was known as {{em|Moynish}}{{#tag:ref|Moynish was variously written as {{langx|ga|m. Nisi, M. Nisse, m. neisi, Magh-Nisi, mMuig Nise, Moigi Nise, Magh-Nise, and Magh-Nissi}}, {{langx|en|Moy-Nissi, Mag Nise, Moynishy, and Moynishe}}, and also called "Upper Muintir Eolais" from the High Middle Ages onwards.{{sfn|Hogan|1910|pp=M}}{{sfn|Ó Donnabháin|1862|pp=xxxviii}}|group="n"|name="m-nisi-name1"}} ("the plain of Nisi") in his honour.{{sfn|Ó Donnabháin|1828|pp=181}}{{sfn|Hogan|1910|pp=M}} Nisi's "honour price" became the perpetual claim by the monastic settlement at Fenagh to patronage from Moynish nobles.
From Cellachan the active,
The proud plain had been named;
Magh-Nissi, manifest famous,
Is its name from that time down.
Their land and their tributes,