• (n.) The quality of being mighty; possession of might; power; greatness; high dignity. • (n.) Highness; excellency; -- with a possessive pronoun, a title of dignity; as, their high mightinesses. Found on http://thinkexist.com/dictionary/meaning/mightiness/
Might'i·ness noun 1. The quality of being mighty; possession of might; power; greatness; high dignity. « How soon this mightiness meets misery.» Shak. 2. Highness; excellency; -- with a possessive pronoun, a title of dignity; as, their high mightinesses... Found on http://www.encyclo.co.uk/webster/M/64