FLATTEN

adj to make vapid or insipid; to render stale.

2. flatten ·adj to lower the pitch of; to cause to sound less sharp; to let fall from the pitch.

3. flatten ·vi to become or grow flat, even, depressed dull, vapid, spiritless, or depressed below pitch.

4. flatten ·adj to reduce to an even surface or one approaching evenness; to make flat; to level; to make plane.

5. flatten ·adj to throw down; to bring to the ground; to prostrate; hence, to depress; to deject; to dispirit.