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.
Eeylops Owl Emporium: A store in Diagon Alley, where Harry got Hedwig.
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.
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".
Enchantment in Baking: A cookbook in Molly Weasley's collection.
Encyclopedia of Toadstools: A book at Flourish and Blotts.
Engorgement Charm: A spell to increase the size of something.
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.
Entrancing Enchantments: Not defined explicitly, but would seem to be spells to produce infatuation.
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".
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.
Evening Prophet: An evening newspaper, probably an alternate edition of the Daily Prophet.
Expelliarmus: The incantation for the Disarming Charm.
Etym: Derived somehow from Latin expellere "drive out, drive away".
Exploding Snap: A wizard card game.