Dictionary? Looking that up in the dictionary, I'd say this was more of an alphabetical list...:)
Letters T-Z have been moved to http://eu.battle.net/wow/en/forum/topic/2394021476?page=3 due to a post limit of 5000 words.
Also at the bottom of that page is a list of dungeon and zones abbreviations - they're also in the "dictionary", but just there as a summariser sort of thing.
WARNING: This post may contain some strong language.
So we all know World of Warcraft slang, more than half the player base uses it because they're too lazy to type with proper punctuation and grammar. (No offense meant.)
I am going to keep track of slang (post if I've forgotten any, or you want to make a contribution). This includes in-game slang like Org (Orgrimmar) etc.
^^ = See above (I agree^) means I agree with the post above, (I agree^^) means I agree with the post two above.
4 = For.
5m = 5 man.
10m = 10 man.
25m = 25 man.
40m = 40 man.
1h = 1 handed.
2h = 2 handed.
AB = Arathi Basin (Battleground available from level 10).
Achiev/Achi = Achievement.
ad/add = Additional monster.
afk = Away from keyboard, Not at computer.
Afaik = As far as I know.
Aggro = Focus of monsters aggresion.
Agi = Agility (stat).
AH = Auction House.
alch/alc = Alchemist (a profession you can learn from a trainer).
alli/ally = Alliance (the faction).
alt = Alternate character (your main is your account with the highest level or most achievement points, or possibly the one you're leveling the most at that time, the rest of them are alts).
AoE = Area of effect (a spell that effects multiple targets within a radius).
AoP/AotP = Aspect of the Pack (hunter spell).
AP = Attack power.
Archi/Archm = Archimonde (Final boss in "Battle for Mount Hyjal", burning crusade raid (I think...?)).
Asap = As soon as possible.
Atm = At the moment.
AV = Alterac Valley (battleground unlocked at (level 40?)).
B4 = Before.
Bb = Bye bye.
Bbl = Be back later.
Bbs = Be back soon.
BC = Burning Crusade.
BE/Belf = Blood elf (Horde race).
Bf = Boyfriend.
Bg/Bgs = Battleground/Battlegrounds (Unlocked at level 10).
BiS = Best in slot (Eg. You have 2 chest pieces, one has 58 armour and the other 20. The 58 armour one is BiS).
BL = Blood Lust (Shaman move).
Blizz = Blizzard, the company that made World of Warcraft.
Blue = Blizzard employee poster, basically on the forums they're the people who's text is blue!
BoA = Bind on account.
BoE = Bind on equip.
BoK = Blessing of Kings (Paladin buff)
BoM = Blessing of Might (Paladin buff)
Boomkin = Moonkin (Balance druid shapeshift spell).
BoP = Bind on pickup.
BoT = Bastion of twilight (Cataclysm raid).
BoU = Bind on use.
BR/Bres = Battle Ressurection (only available to some classes).
Brb = Be right back.
Brt = Be right there.
Bs = Bladestorm - warrior move / Blacksmith (a profession you can learn from a trainer).
Btw = By the way.
Buff = Beneficial spell.
Bwl = Blackwing lair.
Bwd = Blackwing Descent (Cataclysm raid).
Cata = Cataclysm (3rd expansion pack.)
Cba = Can't be ar$ed.
Cbt = Closed beta test.
Cc = Crowd control.
CD = Cooldown.
Char = Character.
Comp = Composition (of whatever it may be), usually used in arena.
CoT = Caverns of time.
Cow = Tauren.
CP = Conquest points Conquest points (Awarded for arena and completing battlegrounds at max level) /Combo points (Rogue and Feral druid only).
Crit = Critical hit.
CR/CRes = Combat resurrection (only available to some classes).
CS = Critical Strike / Counterspell (Mage ability that interrupts an enemy casting a spell).
Cya = See you.
Dal/Dala/Dally = Dalaran, Wrath of the Lich King major city.
Darn/Dar = Darnassus, Night elf capital.
Dc/Dc'd = Disconnect/Disconnected.
DD = Direct damage.
Debuff = Reductionary spell that has an undesirable effect on the player.
Ding = Level up.
Disc = Discipline Priest (Priest healing spec).
DK = Death Knight, Wrath of the Lich King "hero" class.
Dkp = Dragon kill points (used by some guilds for looting system).
Dmg = Damage.
Dnd = Do not disturb.
Dot = Damage over time.
Dpm = Damage per mana.
Dps = Damage per second. (You want this as high as possible!)
Dru/Drood = Druid.
Dtps = Damage taken per second.
DW = Dual wield/Don't worry.
Efc = Enemy flag carrier. (Applies in battlegrounds: Warsong Gulch and Twin Peaks).
Ele = Elemental Shaman (Shaman ranged Dps talent specialization)
Epgp = A point-based loot system used by raids and parties.
En/Enc = Enchanter (A profession available from trainers).
Enc/Enh = Enhancement Shaman (Shaman melee Dps talent specialization).
EoS = Eye of the storm (battleground).
Er = Entangling roots (druid spell).
Expn/Exp/Expan = Expansion, like Cataclysm, Wrath of the Lich King and The Burning Crusade. EDIT: And now Mists of Pandaria!
Ex/Exd = Exodar, Draenei capital.
Exp = Experience gained in-game from killing monsters, handing in quests and completing dungeons and battlegrounds.