The Magic Wand is an item used for casting spells. It is a Wand of Magic.
Alexander was able to discover where Manannan had hidden his wand--the cabinet in his study--and used it to prepare the spells that allowed him to escape, return to Daventry, and destroy the three-headed dragon. He had to be careful with the wand; if he ever forgot to put it back in its place before the wizard returned, he surely would have been killed for his transgression. The wand of Manannan now belongs to the prince, and he used it in preparation for all major spells.
KQ5: The old wand doesn't seem to have any vitality left in it.
KQ7: This wand only has two settings T and F for the use of transforming Trolls into Faeries, or Faeries into Trolls.