v. To understand in a deep and exhaustive manner.
"That new engineer they hired down in IT may be the greatest hardware hacker I've ever seen. The guy simply groks the machine."
This word originated in Robert Heinlein's classic novel "Stranger in a Strange Land", where it was used as a Martian word that meant "to drink" (in its literal sense) and "to be one with" (in its metaphoric sense).
Today's word was suggested, with thanks, by Dan Heller.