It's not the word we use for mum (which is usually
mamma); actually I've never heard "moa" used as a synonym for mum. I would guess it's derived from an old dialectal word for mum, "mora", which sounds more like "moa" in some southern Swedish dialects.
Does the sea exist
Because of our longing?
My PNL
http://www.behindthename.com/pnl/3258/61573