The story
Possibly from neve and/or nephew + -y, but compare (now mostly obsolete) widespread dialectal forms such as /ˈɑːɡi/, /ˈɑɹɡi/ argy (“argue”) and /ˈvali/, /ˈvæli/ vally (“value”) with /i/ for unstressed standard English /juː/.
Etymology from Wiktionary, CC BY-SA 4.0.