mordant

Merriam-Webster's Word of the Day for January 08, 2012 is:

mordant • \MOR-dunt\  • adjective
1 : biting and caustic in thought, manner, or style : incisive 2 : burning, pungent

Examples:
The newspaper columnist's acute insights and mordant wit made her columns a must-read for many subscribers.

"These letters show the tender, funny, love-hungry side of [Philip] Larkin that, in the poems proper, are always in tension with the mordant stuff." -- From a blog post by Adam Gopnik at The New Yorker (online), December 27, 2011

Did you know?
The etymology of "mordant" certainly has some bite to it. That word, which came to modern English through Middle French, ultimately derives from the Latin verb "mordēre," which means "to bite." In modern parlance, "mordant" usually suggests a wit used with deadly effectiveness. "Mordēre" puts the bite into other English terms, too. For instance, that root gave us the tasty "morsel" ("a tiny bite"). But nibble too many of those and you’ll likely be hit by another "mordēre" derivative: "remorse" ("guilt for past wrongs"), which comes from Latin "remordēre," meaning "to bite again."