Oshi is a bit different because, like schadenfreude, it's more of a term that arose out of necessity to cover a large base and hasn't been broken down into individual words for each nuance.
exactly. Most people would translate Otaku as "nerd" or "geek". But a closer translation would be "enthusiast", but even that is kind of.... not exactly it.
A gun otaku is more than a gun enthusiast, for example.