I always thought that Heathcliffe was of Romany/Gipsy/Traveller origin, but can't remember whether this was stated in the book. 'Folksongs of Britain and Ireland (Peter Kennedy) includes songs of the Travellers, the glossary for which the glossary includes 'mither' = mother and 'mulla' = ghost, 'moolin' = killing, 'mulla'= corpse, ghost