The definition was changed by the money changers. It used to mean in Luke Jr bible days just the charging of interest, then they changed it to "unreasonable interest" LOL. Kind of like saying "rape" vs "unreasonable rape". Usury is a form of slavery and it doesn't matter what the yield you're pulling is.
Usury is to lend money with interest. The current banking system was born from it.
Bitcoin, on the contrary, was born from resentment against the banking system, during the 2008-2009 crisis.
Bitcoin still dont have a lending system. So we cant classify it as a usury system, unless your /pol/ dictionary have changed its meaning. But by then, we would be speaking different languages, I guess.