Flat

a. [compar. FLATTER; superl. FLATTEST.] [Icel. flatr, Sw. flat, Dan. flad, O. H. Ger. flaz, allied to Ger. flach, blach, O. H. Ger. flah, Icel. flaki, Gr. πλάξ, Ger. & Sw. platt, D. & Dan. plat, Gr. πλατύς.] 1. Having an even and horizontal surface, or nearly so, without marked prominences or depressions; level without inclination; plain. Though sun and moon Were in the flat sea sunk. Milton. 2. Lying at full length, or spread out, upon the ground; level with the earth; prostrate; hence, fallen; laid low; ruined. What ruins kingdoms, and lays cities flat? Milton. 3. Wanting relief; destitute of variety; without points of prominence and striking interest; monotonous; insipid; stale; dull; frigid. A large part of the work is, to me, very flat. Coleridge.

4. Lacking liveliness of commercial exchange and dealings; depressed; dull.
5. Not relieved, broken, or softened; clear; unmistakable; peremptory; absolute; positive; downright.

Flat burglary as ever was committed. Shak. A great tobacco-taker too, — that's flat. Marston.

6. (Mus.) (a.) Below the true pitch; hence, as applied to intervals, minor, or lower by a half-step; as, a flat seventh. (b.) Not sharp or shrill; not acute; as, a flat sound.
7. (Pron.) Uttered with voice instead of breath; spoken, in distinction from whispered; vocal; sonant; — said of certain consonants in the production of which the larynx is brought into action, as b, d, v, z, &c., as distinguished from p, t, f, s, &c.

n. 1. A level surface, without elevation, relief, or prominences; an even or plain space of ground; a low tract. Envy is as the sunbeams that beat hotter upon a bank, or steep rising ground, than upon a flat. Bacon. 2. A level tract lying at little depth below the surface of water, or alternately covered and left bare by the tide; a shoal; a shallow; a strand. Half my power, this night Passing these flats, are taken by the tide. Shak.

3. Something broad and flat in form; as, (a.) A flat-bottomed boat, without keel, and of small draught. (b.) A straw hat, broad-brimmed and low-crowned. (c.) (Railway Mach.) A car without a roof; a platform car.
4. The flat part, or side, of any thing; as, the broad side of a blade, as distinguished from its edge.
5. A floor, loft, or story in a building. [Scot.]
6. A dull fellow; a simpleton; a numskull.

Or if you can not make a speech, Because you are a flat. Holmes. 7. (Mus.) A character [♭] before a note, indicating a tone which is a half-step or semitone lower.

v. i. 1. To become flat, or flattened; to be reduced from a prominent or elevated to a level surface. Temple.

2. To become insipid, or dull and unanimated. [Obs.] King Charles.
3. (Mus.) To fall from the pitch.

To flat out, to fall from a promising beginning; to make a bad ending; to disappoint expectations.