A spell in the Harry Potter series that cuts the target several times like a sword. It was invented by Severus Snape and chronicled in his annotated Potions schoolbook, where Harry Potter learned it. The cuts can only be healed immediately after infliction by a countercurse also created by Severus Snape.
The spell is ineffective on Inferi or other creatures who do not have or need blood.
The name derives from the Latin sectum, "cut", and semper, "always"
Harry Potter dropped Draco Malfoy like a convulsing brick by slashing him with the effects of Sectumsempra.