From nain (from reanalysis of an own, mine own etc. as a nain, my nain) + sell, alternative form of self.
nainsell
- (Scotland, obsolete) self
1902, William MacLeod Raine, A Daughter of Raasay[1]:"Gin ye hae your appetite wi' you we'll eat, Mr. Montagu, for I'm a wee thingie hungry my nainsell (myself).
1806, Walter Scott, Minstrelsy of the Scottish Border, Vol. II (of 3)[2]:Forsooth her nainsell lives by thift.