Altered from Maniske, from assumed Old Norse *manskr, an adjectival form of Mǫn (“Isle of Man”), from Old Irish Mana; compare with Norwegian Bokmål mansk.
The cause was, he courted a pretty Manks maid who lived in a bower beneath the blue tree of Glen Aldyn, and therefore was absent from the Fairy court during the Re-hollys vooar yn ouyr, or harvest-moon, being engaged dancing in the merry glen of Rushen. 1850, Thomas Keightley, The Fairy Mythology, London: H.G. Bohn, page 403:
[…] the others marry with the Manks women, so their children become natives. c. 1648, William Blundell, A History of the Isle of Man:
Altered from Maniske, from assumed Old Norse *manskr, an adjectival form of Mǫn (“Isle of Man”), from Old Irish Mana; compare with Norwegian Bokmål mansk.
Those who reckon the extirpation of the Manks language to be a necessary step towards the general extension of English which they deem essential 1835, Archibald Cregeen, Dictionary of the Manks Language: