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Webster 1913 Edition

Noun.

The quality of being mighty; possession of might; power; greatness; high dignity.

How soon this

mightiness

meets misery.

Shakespeare

Highness; excellency; – with a possessive pronoun, a title of dignity;

as, their high

mightinesses

Noun.

Power; greatness; highth of dignity.

How soon this mightiness meets misery!

A title of dignity; as their High Mightinesses.

mightiness ‎(uncountable)