coined by Heinlein in 1961, grok actually found its way into the 2nd edition of the OED, marked as U.S. slang:

a. trans. (also with obj. clause) To understand intuitively or by empathy; to establish rapport with. b. intr. To empathize or communicate sympathetically (with); also, to experience enjoyment.

therein are some fine citations, but I really enjoyed the last: 1984 InfoWorld 21 May 32 "There isn't any software! Only different internal states of hardware. It's all hardware! It's a shame programmers don't grok that better."