Reducio

Reducio is the natural counterweight to Engorgio — the Shrinking Charm that reverses the Engorgement Charm and returns swollen objects to their original dimensions. Latin reducere again, the same root that gives the offensive Reducto, but with an entirely different application. Where Reducto pulverizes, Reducio simply restores.

Reducio is taught as the second half of the Engorgio pair in fourth-year Charms, and most students learn the two charms as a single fluent skill. The cast is straightforward — same wand movement as Engorgio, same intent in reverse — and is typically practiced by enlarging and then reducing a single textbook object until both halves of the cycle feel automatic.

Importantly, Reducio is bounded. The charm will return an Engorgio'd object to its natural size and stop there. It will not continue shrinking past the original dimensions, so you cannot use Reducio to make a normal teacup into a doll's teacup. Genuinely shrinking an object below its baseline requires the dedicated Shrinking Charm — Diminuendo and its variants — which is a different spell with different mechanics.

In daily practice, Reducio shows up most often as the silent partner to whatever Engorgio just happened. Mad-Eye/Crouch shrinks the spider back down. Hagrid restores the harvest pumpkin he was demonstrating. The Weasleys reset whichever joke product they were testing. The charm's purpose is restoration rather than transformation, which is exactly why it sits comfortably in the everyday curriculum.