different between braininess vs greatness

English

brainy +? -ness

braininess (uncountable)

From Middle English gretnesse, gretnes, greetnesse, from Old English gr?atnes. Equivalent to great +? -ness.

greatness (countable and uncountable, plural greatnesses)

The state, condition, or quality of being great
Due to the greatness of his size, he was an effective bodyguard.
greatness of mind
- c. 1600, William Shakespeare, Twelfth Night ACt 3 Scene 4
  Some are born great, some achieve greatness, and some have greatness thrust upon 'em.
(obsolete): Pride; haughtiness.
- 1627, Francis Bacon, New Atlantis
  It is not of pride or greatness that he cometh not aboard your ships.

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