DerHauptman said:
verisimilitude (don't remember probably 1eDMG)
That's the one that came right to mind, first.
I also learned the difference between "rogue" and "rouge" when 3rd Edition came around. Man, I hated having to go though all my Word files to replace everywhere it said "rouge" with "rogue".
Portcullis and ziggurat are also good choices.
And who could forget paralyzation and polymorph after 2nd Edition came out.
Other words I learned from D&D: Abyss, griffon/griffin, concordance, ogre, samurai & ronin, katana, Sumurian, Babalyon, proficiency, morningstar, phylactery, conjuration, abjuration, illusion, astral, ethereal, Limbo, Elysian, norse, Excalibur, etc.
I could go on and on, but i won't.
KF72