Flattens stairs treads, creating a slide.
- "...Hermione shouted, 'Glisseo!' The stairs beneath their feet flattened into a chute..."
- —Hermione Granger's use of the spell in the Battle of Hogwarts[src]
Glisseo is a spell that causes the treads of stairs to flatten, turning the stairs into a slide or ramp. Hermione Granger used this spell to transform a staircase into a slide during the Battle of Hogwarts so that she, Harry Potter and Ronald Weasley could avoid an attack by some Death Eaters. This may be the spell used on the girls' staircases at Hogwarts to prevent boys from entering, as the effects (when activated) are the same.
The spell's incantation originates from the French verb, 'Glisser', meaning "to slip" or "to slide".