In Irish mythology, Nemain (modern spelling: Nemhain) is the fairy spirit of the frenzied havoc of war, and possibly an aspect of the Morrígan. The name is sometimes spelt Nemon or Neman.

In the grand Irish epic of the Tain Bo Cuailnge, Neman confounds armies, so that friendly bands fall in mutual slaughter. When the forces of Queen Medb arrive at Magh-Tregham, in the present county of Longford, on the way to Cuailnge, Neman appears amongst them:

“Then the Neman attacked them, and that was not the most comfortable night with them, from the uproar of the giant Dubtach through his sleep. The bands were immediately startled, and the army confounded, until Medb went to check the confusion.” Lebor na hUidhre, fol. 46, b1.

And in another passage, in the episode called “Breslech Maighe Muirthemhne,” where a terrible description is given of Cuchullain’s fury at seeing the hostile armies of the south and west encamped within the borders of Uladh, we are told (Book of Leinster, fol.54, a2, and b1):

“He saw from him the ardent sparkling of the bright golden weapons over the heads of the four great provinces of Eriu, before the fall of the cloud of evening. Great fury and indignation seized him on seeing them, at the number of his opponents and at the multitude of his enemies. He seized his two spears, and his shield and his sword, and uttered from his throat a warrior’s shout, so that sprites, and satyrs, and maniacs of the valley, and the demons of the air responded, terror-stricken by the shout which he had raised on high. And the Neman confused the army; and the four provinces of Eriu dashed themselves against the points of their own spears and weapons, so that one hundred warriors died of fear and trembling in the middle of the fort and encampment that night.”