So this is what I’ve come up with.
Geek — someone who is highly, even overly, enthusiastic about a particular field of endeavor or interest. More than hobbyists, geeks are several ranks up from buffs. Usually, equipment or materials are involved, as in: camera geek, yarn geek, car geek, silent movie geek. Has to be non-sentient, too: someone who’s avid about people they don’t personally know would be either a fan, groupie or stalker. So, one can be a rock geek, a star geek, but not a rock-star geek.
Geeks love to hang out with other geeks of their persuasion, witness camera clubs, yarn-off evenings and Trekkie Conventions (Trekkies are geeks not fans because their focus is the whole show, not just the stars). A geek’s concentration, while it might seem somewhat whacked to their significant others, nevertheless can be genially tolerated and should even be indulged. If it’s an irritant, then look out, that relationship is OVER. While geeks will gladly talk shop whenever possible, they are also willing and able to converse on other topics and they will participate in other activities, such as work that might not be their enthusiasm, raising the kids, attending family functions. In the best of all possible worlds, some one, a nephew, niece, grandparent, in-law, uncle or aunt, is also smitten by the same bug, and the long afternoon barbeques pass in a lovely haze of shared enthusiasms.
Although those who know me might disagree, I self-identify as a word-geek. I love words and how they operate; I love them forwards, backward, sideways, jumbled-up, scrabbled. New words thrill me; making them up is even better. Anagrams, puns, poems; bring them on. A word geek like myself either has the OED or lusts after one. But a word nerd no longer needs one; they have it memorized and can recite definition and antecedent, first print appearances, annotations, footnotes, and variance of usage across time. We need the word-nerds of the world to keep the dictionaries well-oiled and running. Then we word-geeks can have the fun of pushing them to their limits.