Is Akbar a name of Allah?

Al-Kabeer is a name of Allah what about Akbar? Can we say it's not a name of Allah if it's not found in the Quran or Sunnah or should we need to say I cannot affirm it because it's not found in Quran or Sunnah. In this situation can a Muslim deny this as name of Allah because it's not found in the Quran or Sunnah is it kufur? Because we know Allah has many names and We know few of them through Quran and Sunnah we don't know remaining.