\Flat"ness\, n.
1. The quality or state of being flat.

2. Eveness of surface; want of relief or prominence; the
   state of being plane or level.

3. Want of vivacity or spirit; prostration; dejection;
   depression.

4. Want of variety or flavor; dullness; insipidity.

5. Depression of tone; the state of being below the true
   pitch; -- opposed to {sharpness} or {acuteness}.