I guess I'm behind again. Just found out that the word Grok comes from a science fiction novel. I guess I always thought that 'grok' came from some Unix pun like GNU.
:grok: /grok/, var. /grohk/ vt. [from the novel "Stranger in a Strange Land", by Robert A. Heinlein, where it is a Martian word meaning literally `to drink' and metaphorically `to be one with'] The emphatic form is `grok in fullness'. 1. To understand, usually in a global sense. Connotes intimate and exhaustive knowledge.
-- The Jargon File 3.2.0