the Jester
Legend
There are actually a couple of items that give a lesser property whether you're attuned or not, but only gain additional properties if you are attuned to that. Given that, I'd rule that a weapon that requires attunement for all its properties doesn't count as magic if you aren't attuned. (I'm pretty sure there is at least one magic weapon like that in the DMG, but don't recall off hand which one it is.)