Reducing charm
Incantation: Reducio
Pronunciation: re-dew-see-oh
Description: Makes an enlarged object smaller. Counter-charm to Engorgio.
Seen: Used in GoF by Barty Crouch Jr (as Moody) to shrink the spider he used to demonstrate the Cruciatus Curse. Harry attempts the spell in the Deathly Hallows when practising with Draco's blackthorn wand.

Reductor Curse
Incantation: Reducto
Pronunciation: re-duk-toh
Description: Enables the caster to explode solid objects.
Seen: In GoF, Harry uses it on one of the hedges of the Triwizard maze and ends up burning a small hole in it. In OotP, Gryffindors in Harry's year reference Parvati Patil as being able to reduce a table full of dark detectors to ashes and Ginny Weasley uses it in the Room of Requirement during the practice and in the Hall of Prophecy, Department of Mysteries. In HBP, a member of the Ootp attempts to use this spell to break down a door which Death Eaters have blocked when the Death Eaters have cornered Dumbledore in the Lightning Struck Tower.

Refilling Charm
Incantation: Unknown
Description: Refills whatever at which the caster points with the drink originally in the container.
Seen: Used in HBP, when Harry notices that Hagrid and Slughorn are running out of mead.

Relashio
Incantation: Relashio
Pronunciation: re-lash-ee-oh
Description: A charm used to force someone or something to release that which it holds or grapples by means of shooting fiery sparks out or, underwater, shooting hot bursts of water.
Seen: Used by Harry against Grindylows in the second task of the Triwizard Tournament. Hermione uses it in Deathly Hallows to free Mrs Cattermole from the chained chair.

Rennervate
Incantation: Rennervate
Pronunciation: ren-ər-vayt
Description: Brings someone out of unconsciousness. Counter spell to the stunning jinx.
Seen: In GoF, Amos Diggory uses it to wake Winky up and Dumbledore uses it to wake Krum and Barty Crouch Jr up. In HBP, Harry later uses it to try to reawaken a cursed Dumbledore in the seaside cave.

Repairing charm
Incantation: Reparo
Pronunciation: re-par-oh
Description: Used to repair broken or damaged objects.
Seen: Many times throughout the books. Shattered objects are often described as having "flown" back together. However, substances contained within broken objects are not restored.
Notes: Harry used this spell twice to repair his wand in Harry Potter and the Deathly Hallows, once with a normal wand and a second time with the "Elder Wand" or "Wand of Destiny". Only the second attempt was successful.

Repelling Charm
Incantation: Unknown
Description: Pushes a moving object away from an invisible barrier.

Muggle-Repelling Charm
Incantation: Repello Muggletum
Pronunciation: re-pel-oh mug-lə-təm
Description: Keeps Muggles away from wizarding places by causing them to remember important meetings they missed and/or to cause the Muggles in question to forget what they were doing there in the first place.
Seen: Harry and Hermione also use it on numerous occasions, among many other spells, to protect and hide their campsite in Deathly Hallows.

Tickling Charm
Incantation: Rictusempra
Pronunciation: rik-tə-sem-prə
Description: The subject experiences the sensation of being tickled
Seen: First seen used by Harry on Draco in Chamber of Secrets, when they fought in the Duelling Club. This spell takes the form of a jet of silver light.

Boggart-Repelling Charm
Incantation: Riddikkulus
Pronunciation: ri-dik-ə-ləs
Description: A spell used when fighting a Boggart, "Riddikulus" forces the Boggart to take the appearance of an object upon which the caster is concentrating. When used correctly, this will be a humorous form.
Seen: First seen in PoA, when taught by Lupin. Then seen in GoF on a boggart that was in the maze in the Third Task. Finally seen in OotP, when Mrs Weasley tries to cast Riddikulus on a Boggart in Grimmauld Place.