A brand or, now, a generic term for a thick nibbed, colored-ink pen usually with washable, water-based ink. Also, a tool in Nethack which can be used to create any kind of scroll when applied to a blank scroll.

In NetHack, magic markers can also be used to write spellbooks when applied to blank spellbooks. Probability of success is significantly higher if the spell is known and if the user is a wizard. A magic marker is a popular item to wish for with a wand of wishing or random wishes granted from thrones, fountains, etc.

To blank a scroll or spellbook, dip it in water. Blessing your magic marker and your media isn't a bad idea either.