IJK

Impediment Curse ~ To slow down and obstruct attackers; impedimenta is the incantation. [4,31]

Imperio ~ The Imperius curse; gives a wizard total control over another life. An Unforgivable Curse. [4,14]

Imperturbable Charm ~ Renders an object safe from disturbance - or spying. [5,4]

Impervius ~ A charm to make an object repel water. [3,9]

Incarcerous ~ A spell that causes ropes to secure an object - or person. Or creature. [5,33]

Incendio ~ A cahrm to start a fire. [4,4]

Inferius ~ A corpse bewitched to do a Dark Wizard's bidding; inferi were used by Lord Voldemort, who "killed enough people to make an army of them". [6,3]

Inquisitorial Squad ~ A select group of students, supportive of the Ministry for Magic , hand-picked by Professor Umbridge. [5,28]

Invisibility Booster ~ Device to ensure invisibility, of a Ford Anglia, for example. [2,5]

Invisibility Cloak ~ Allows wearer to proceed unseen; except for certain wizarding devices that might reveal the wearer. And cats, possibly. [1,12]

Jelly-Legs Jinx ~ Does as it says! [4,31]

Arsenius Jigger ~ Author of Magical Drafts and Potions. [1,5]

Angelina Johnson ~ Chaser for Gryffindor's Quidditch team. [1,11]

Gwenog Jones ~ Captain of the Holyhead Harpies Quidditch team. [6,4]

Hestia Jones ~ Pink-cheeked, black-haired witch. [5,3]

Lee Jordan ~ The Weasley twins' best friend at Hogwarts. [1,6]

Bertha Jorkins ~ A missing witch. [4,1]

Jugson ~ A Death Eater. [5,35]

Kappa ~ Water dweller that seeks to strangle. [3,8]

Professor Igor Karkaroff ~ Head of Durmstrang School. [4,15]

Karkus ~ Gurg for a while. [5,20]

Keeper ~ In Quidditch, the Keeper flies around the Hoops to stop the other team scoring. [1,10]

Dementors' Kiss ~ Their final weapon: excision of the soul. [3,12]

Kneazle ~ A cat-like creature with an uncanny ability to detect suspicious characters. They can interbreed with cats. [FB&wtft]

Knight Bus ~ A triple-decker omnibus, emergency transport for the stranded witch or wizard. [3,3]

Knockturn Alley ~ An undesirable area near Diagon Alley. [2,4]

Knut ~ A little bronze coin (493 to one Galleon, 29 to one Sickle). [1,5]

Kreacher ~ House Elf for the Black household. [5,4]

Viktor Krum ~ Star Quidditch player from Bulgaria. [4,5]

KwikSpell ~ A correspondence course in magic for beginners. [2,8]