Diffindo

Diffindo is the textbook Severing Charm — Latin diffindere, "to split, divide, cleave." Cast at a target, it produces a clean, shallow cut along whatever the wand is aimed at. The charm is taught in fourth-year Charms and is part of the standard practical exam curriculum, sitting alongside the Summoning Charm and the Banishing Charm as everyday Charms-class staples.

What Diffindo does well, it does very well: cutting fabric, rope, parchment, twine, ribbon, leather. It's the spell you reach for when your bag's strap snaps and you don't want to sew, when a rope needs to be parted in a hurry, when a piece of paper has to be cleanly torn. Hermione famously uses it on Harry's school bag in the Goblet of Fire to give Cedric an oblique nudge about the first task. The cut is precise enough to look intentional, which is often the entire point.

Power and range scale with the caster. A weak Diffindo grazes, a confident one cleanly slices, and a strong wizard can sever heavier materials at distance. It is not, however, a duelling spell. Cast at a person, Diffindo can produce a shallow gash, but for actual combat against a witch or wizard the curriculum reaches for Sectumsempra-class curses or Stunning Spells. Diffindo is a craftsman's tool, not a soldier's.

The charm has a quiet relationship to Sectumsempra, the Snape-invented dark cousin that produces sword-deep wounds rather than shallow cuts. Diffindo and Sectumsempra share a root and an effect, but they sit on opposite sides of the curriculum's moral line — one a Hogwarts staple, the other a curse marked "For Enemies" in a clever student's marginalia.