The word pharaoh ultimately derive from the Egyptian compound "great house," written with the two biliteral hieroglyphs "house" and "column", here meaning "great" or "high".
The earliest instance where pr-ˤ3 is used specifically to address the ruler is in a letter to Amenhotep IV (Akhenaten), who reigned circa 1353-1336 BCE, which is addressed to "Pharaoh, all life, prosperity, and health" [REF].