Milton.
3. (Fine Arts) Wanting relief; destitute of variety; without points of
prominence and striking interest.
A large part of the work is, to me, very flat.
Coleridge.
4. Tasteless; stale; vapid; insipid; dead; as, fruit or drink flat to
the taste.
5. Unanimated; dull; uninteresting; without point or spirit;
monotonous; as, a flat speech or composition.
How weary, stale, flat, and unprofitable Seem to me all the uses of
this world.
Shak.
6. Lacking liveliness of commercial exchange and dealings; depressed;
dull; as, the market is flat.