American Heritage Dictionary
(1)
Century Dictionary
GNU Webster's 1913
WordNet
(1)
Elsewhere on the web
At the risk of making vast racial stereotypes, I felt that I understood most of the major cultures in the world, but the Muslim culture was one that I simply couldn't "grok" well.— Joi Ito's Web
Please excuse my ignorance, but what does "grok" mean?— The Full Feed from HuffingtonPost.com
Simplicity makes your analysis clearer and easier to grok.— tante's blog
Most people, though, simply do not grok how much data a short video or a few dozen lightly compressed photos use up, though.— Slashdot: Hardware
Scott asked insightful, well-thought-out questions: It's always nice to see a journalist and author really grok how creative work is being carved out by independent artists online.— Sheldon Comic Strip: The daily webcomic by Dave Kellett

American Heritage Dictionary (1)
Bubble size: how much this word was used in a year
Bubble height: used more or less than expected, vs. all uses evenly distributed
You can expect to see this word about twice a year.