ETYMOLOGY
either an alteration of Norse (adj.) after Scottish, or directly from Norwegian norsk (Norse), with suffix substitution
EXAMPLE
“… for he was in prayer more frequent then yong ones are usually seen to be, of a spare diet, and so compassionate of the poor, as all that came in his hands he distributed among them: Servanus his Master loving him beyond others, was ordinarily wont to call him Mongah, which in the Norish tongue, signifieth a deare friend; and this way came he to be called Mungo. …”
From: The History of the Church of Scotland, beginning in the year of our Lord 203 and continued to the end of the reign of King James the VI
By John Spottiswood, 1677
Lexicophilia 