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"mountain ash," 1804, from rowan-tree, rountree (1540s), northern English and Scottish, from a Scandinavian source (cf. Old Norse reynir, Swedish Ronn "the rowan"), ultimately from the root of red, in reference to the berries.
There were those in this neighbourhood, long after the beginning of the present century, who believed that a slip of rowan tree carried on their person dispelled glamour, and rendered nugatory all the powers of sorcery and witchcraft. [Alexander Laing, "Lindores Abbey and the Burgh of Newburgh," Edinburgh, 1876]