Definition of high and mightiness in US English:

high and mightiness

noun

  • 1With possessive adjective. A title of respect or respectful form of address given to a person of high rank or status; specifically a title given to a member of the States General of the Netherlands (now historical). Also as a mock title, especially given to a person considered to affect an air of superiority.

  • 2The quality of being high and mighty; high rank or status; (now usually) arrogance, superciliousness.

Origin

Mid 17th century; earliest use found in Mercurius Pragmaticus. From high + and + mightiness, after high and mighty.