Melia does not mean 'ash tree'. The Meliae were nymphs of the ash tree, but they got their name from the sweet honey-like sap. From Wikipedia:"Many species of Fraxinus, the ash trees, exude a sugary substance, which the ancient Greeks called méli, "honey". The species of ash in the mountains of Greece is Fraxinus ornus, Manna-ash. The Meliae were nurses of the infant Zeus. They fed him honey."