... If it’s an outdoor interest ...
Besides trainspotting, what counts as an “outdoor interest”? For example, I’m guessing that enthusiasts of sports are not “anoraks”.
You can be an anorak if you’re heavily into the statistics of sport - this gentleman might be an example. (There isn’t, curiously, afaik, a Rightpondian equivalent of the Leftpondian term “jock”, for “hearty sports enthusiast.")
It seems to me that while “nerd” covers any non-sporty male lacking in social skills and with limited fashion sense, “geek” generally applies specifically to a nerd with obsessive technological interests, often of a practical or money-making application, while “anorak”, as used in Rightpondia, is used of a nerd whose obsessions are frequently arcane and generally of no practical application. Wikipedia is, I think, pretty good on explaining the term.
While “anorak” as an expression seems to have sprung originally from trainspotters (and their close relatives, aircraft spotters), who wore anoraks to protect themslves from the elements, it is used of persons (almost always male) showing obsessive interest in any trivial area of study from beer mat collecting to science fiction, not least because they frequently wear anoraks too, combining the nerd’s desire for the comfortable with his lack of fashion sense.
Sone specific sorts of “anorak” have their own designations: bird-watchers who are obsessive collectors of sightings are called “twitchers”, while persons who obsessively collect tastings of new microbrewery beers are called “tickers” or “scoopers”.
There is, of course, no such thing as a “word nerd”, all persons interested in etymology being thoroughly rounded invididuals with impeccable fashion sense and extremely busy social lives who are naturally highly attractive.
Incidentally, while the anorak - which strictly should be a garment with no front opening, pulled over the head - has never been fashionable, the parka, longer and with a front opening, became a fashion icon because of its association with mods, who wore them to protect their clothes while riding their Vespa or Lambretta scooters - as in the film Quadrophenia