ebony: Wood from several tree species in the genus Diospyros, favored for its durability, hardness, and ability to take high polish. In India it was used for drinking cups for its supposed ability to neutralize poison. Use these days is mainly decorative.
Eddie Carmichael: Etym: From Old English ead "rich, happy" + weard "guardian".
Edgar Bones: Etym: From Old English Eadgar "rich, happy".
Edgecombe, Marietta (OotP ch. 18): A friend of Cho Chang, probably a Ravenclaw, who spilled the beans on Dumbledore's Army.
Etym: Couldn't find anything specific, but probably from a name for a person living on the edge of a valley.
Educational Degree Number Twenty-eight (OotP ch. 28): The one that made Umbridge the headmistress.
Educational Degree Number Twenty-five (OotP ch. 19): The one that gave the High Inquisitor supreme authority over all punishments given to Hogwarts pupils.
Educational Degree Number Twenty-four (OotP ch. 17): The one that restricted freedom of assembly to approved student groups.
Educational Degree Number Twenty-nine (OotP ch. 28): The one that Filch thought would bring back corporal punishment.
Educational Degree Number Twenty-seven (OotP ch. 26): The one to expel any student caught in possession of The Quibbler.
Educational Degree Number Twenty-three (OotP ch. 15): The one that created the post of Hogwarts High Inquisitor.
Educational Degree Number Twenty-two (OotP ch. 15): The one that gave the Ministry of Magic the power to select a teacher when the headmaster cannot.
Eeylops Owl Emporium: A store in Diagon Alley, where Harry got Hedwig.
elderflower wine: Can mean wine made from elderberries or elderberry flowers combined with some other fruit.
Eleanor Branstone: Etym: From a Provençal form of Helen, Greek for "the bright one". The name of several queens.
Elephant and Castle (OotP ch. 7): The site of one of the regurgitating toilet pranks; a popular part of London.
Elfric the Eager (PS ch. 16): The leader of a notable historical uprising.
Etym: From the Old English words for "elf" and "ruler".
Elixir of Life: A formula that extends the lifespan indefinitely, made possible with a Philosopher's Stone.
Elfrida Cragg: Etym: From Old English ælf "elf" + thryth "strength".
Elladora (Black?): Etym: None found.
Eloise Midgen: Etym: From Old German haila "hale, sound" + vid "wide".
Emeric the Evil: Some historical personage who could be confused with Uric the Oddball.
Etym: From an Old German root Im- or Em-, of unknown meaning, + ric "ruler". Also, emerick is an obsolete alternate form of emery.
Emeric Switch: Etym: See above.
Emma Dobbs: Etym: A hypocoristic form of various Old German names combined with ermin/irmin "whole, universal".
Emmeline Vance: Etym: From a diminutive form of amal- "work".
Enchantment in Baking: A cookbook in Molly Weasley's collection.
Encyclopedia of Toadstools: A book at Flourish and Blotts.
Enervate: An incantation to revive an unconscious person.
Etym: English. Spelled ennervate in some first editions, but one n is correct.
Engorgement Charm: A spell to increase the size of something. Incantation: Engorgio.
Engorgio: Incantation for an Engorgement Charm.
Etym: Pseudo-Latin, "I (cause to) engorge". The imperative form would be engorgere or engorgire "become engorged".
Enid (PS ch. 7): Neville Longbottom's great-aunt.
Etym: Celtic name of uncertain derivation. In Arthurian legend, the wife of Geraint, noted as an example of long-suffering patience.
Enlarging Spell (OotP ch. 23): A spell that makes something bigger inside than out.
Entrail-Expelling Curse (OotP ch. 22): What it sounds like, I guess.
Entrancing Enchantments: Not defined explicitly, but would seem to be spells to produce infatuation.
Eric Munch: Etym: An unknown element + ric "ruler, government". Also an obsolete word for blood money.
Erised stra ehru oyt ube cafru oyt on wohsi: The inscription on the Mirror of Erised, describing soed ti tahw.
Ernie Macmillan [Ernest] (CoS ch. 11):
Etym: From Old German Ernust "vigor, earnestness".
Etym: See above.
Errol (CoS ch. 3): The Weasleys' owl.
Etym: From Latin errare "to wander". Hints also of Errol Flynn.
Eton: The most exclusive secondary school in England; Justin Finch-Fletchley still picked Hogwarts over it.
Euan Abercrombie: Etym: Probable variation of Evan.
Europa (OotP ch. 14): One of the Galilean moons of Jupiter.
Evan Rosier: Etym: From a Welsh form of John, from Hebrew Johanan, meaning "Jehovah has favored".
Evanesco (OotP ch. 5): Etym: Formed from Latin evanescere "to vanish like vapor".
Evans Dursley, Petunia: Etym: See Evan.
Evans, Mark (OotP ch. 1): A ten-year-old that Dudley Dursley and his gang beat up.
Etym: See Evan.
Evans Potter, Lily: Etym: See Evan.
Evening Prophet: An evening newspaper, probably an alternate edition of the Daily Prophet.
Everard (OotP ch. 22): A previous headmaster of Hogwarts.
Etym: From Old German ebur "boar" + hardu "hard".
Ever-Bashing Boomerangs: Something from the long list of items students are banned from bringing into Hogwarts.
Expecto Patronum: Incantation to summon a Patronus.
Etym: From Latin exspecto "I expect" (literally "look forward to") and patronus, "patron, defender".
Expelliarmus: The incantation for the Disarming Charm.
Etym: Derived somehow from Latin expellere "drive out, drive away".
Expellimellius (OotP ch. 18): A fumbled incantation for a Disarming Charm that instead resulted in an arm catching fire.
Etym: Just a gibberish form, I guess.
Exploding Snap: A wizard card game.
Extendable Ears (OotP ch. 4): An eavesdropping aid produced by Weasley's Wizard Wheezes.
Extinguishing Spell: A spell to put out fires.