The term 'Tree Sacred to the Druids' refers to three trees: ALDER (5 letters), OAK (3 letters), and YEW (3 letters). ALDER is a deciduous tree that is native to Europe, North Africa, and western Asia. OAK is a type of hardwood tree that is native to temperate regions of the Northern Hemisphere. YEW is an evergreen tree that is native to Europe, North Africa, and western Asia. All three of these trees were considered sacred by the Druids, an ancient Celtic religious order.