Arc! The only thing it's a reference to is that it's the name of one of my OC for a game that I've been working on, Arc. I really liked the name, so I just thought "might as well have my PC username, Arc, right?".
I wasn't totally on board on renaming my username to Arc since I was actually contemplating between Arc, Arcaia, or Lehaut . But I eventually settled on Arc, haha.