i Register
In some senses, highness is marked as obsolete. Watch for register when choosing this word.
noun
The state of being high.
'It is as high as heaven, what canst thou do?' It is as the highnesses of heaven: take all the heights and elevations, all the spheres and altitudes of heaven, and try if thou canst reach them with thy short arm; yea, climb up the highest storeys, the loftiest pinnacles, […]
A title of respect when referring to a prince or princess.
noun
The style of a prince, princess or someone of equivalent rank.
The style of an emperor or king.