Vulnera Sanentur

"[...] he knelt over Malfoy, drew his wand and traced it over the deep wounds Harry's curse had made, muttering an incantation that sounded almost like song. The flow of blood seemed to ease; Snape wiped the residue from Malfoy's face and repeated his spell. Now the wounds seemed to be knitting."

- Description

Vulnera Sanentur was the song-like incantation of a healing spell and counter-curse to the Sectumsempra Spell, both of which were invented by Professor Severus Snape under his alias of "Half-Blood Prince".

Effect
For maximum effect of the spell, the incantation had to be repeated thrice; firstly slowing the flow of blood to prevent death by exsanguination; the second to clear residue and begin to heal the wounds; and the third to fully knit the wounds, although dittany had to be applied to prevent scarring.

Known uses

 * Albus Dumbledore healed a wound made to his hand in the Crystal Cave using this spell.
 * Poppy Pomfrey repaired a nasty cut to Harry Potter's shoulder with this after he was attacked by a Hungarian Horntail in the First Task of the Triwizard Tournament
 * When Draco Malfoy was attacked by Harry using Sectumsempra, the damages inflicted were reversed by Severus Snape with his charm.

Etymology
Vulnera Sanentur derives from the Latin vulnus, "wound," (in which the roots of the English "vulnerable" may be seen) and sanare, "to heal"; it is translated "may the wounds be healed."

Behind the scenes

 * Body parts that had been completely removed with Sectumsempra could not be restored even using this spell.
 * In the book, Harry stayed in the bathroom after cursing Malfoy and witnessed Snape's use of the spell; in the film he ran straight to the common-room.

Appearances

 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (film)