Why did the Egyptians call their king pharaoh? A. The Egyptians borrowed the title from the Sumerians. B. The king wore the Double Crown of Egypt, and the word means "he who rules all." C. Thinking it was disrespectful to speak directly about a god-king, they referred to the palace instead. D. Calling such a powerful ruler king was not enough, and the word pharaoh means god-king.
Initially word pharaoh meant as much as the "Great House", however later it evolved in a way it also meant a "God-King". So I assume the correct answer is C - Egyptians referred to the king's palace as it was disrespectful to speak directly.
