"To 'spell' a word, we have to cast a spell or charm over it, to bring the letters into place so as to compel its meaning to appear, or cast a magic spell over the word, or bring together the letters which are potent to dissplve or unravel speech."  From Symbolic Mythology and Translation of a Lost and Forgotten Language by John Martin Woolsey, 1917.   Very much of interest: The Young Wizard's Hexopedia.