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"