Definition of "Flatness" :

noun: inactivity; showing an unusual lack of energy

noun: the property of having little or no contrast; lacking highlights or gloss

noun: the property of having two dimensions

noun: a deficiency in flavor

"It needed lemon juice to sharpen the flatness of the dried lentils."

noun: a want of animation or brilliance

"The almost self-conscious flatness of Hemingway's style."