All of the new words I found this week came from The Grail War, which I am still trudging through (almost done!) You can visit Bermudiaonion's weblog to see what new words other readers have discovered.
Spang- "Prang saw Parsival move: a blur, a flying shadow, a flashing of steel, spangs, crunchings, screams, sighs, curses, men scattering and falling like rats before a striking cat."
Definition: To leap, cast, jerk or bang. It can also be an adverb meaning precisely, exactly.
Putative: "...he stayed and resisted and frustrated his putative master."
Definition: Inferred, or or accepted as true on inconclusive grounds (implying it wasn't his true master?)
Sardonic: "She shook her sardonic head."
Definition: Scornfully or cynically mocking
Nonce: " 'I care little for the nonce, whether it be demons or mooncalfs you follow.' "
Definition: The present or particular occasion
Laconically: " 'This is my command,' he said laconically. 'Who in hell asks?'"
Definition: Using few words, terse or concise
Vagary: "Because of a vagary in the air currents, the fog was thinner here."
Definition: An extravagant or erratic notion or action