Webster's Revised Unabridged Dictionary · 1913

Flat

Flat (flat) , adjective

[Akin to Icelandic flatr, Swedish flat, Danish flad, Old High German flaz, and Anglo-Saxon flet floor, German flotz stratum, layer.]

1.
Having an even and horizontal surface, or nearly so, without prominences or depressions; level without inclination; plane.
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 ground or earth; prostrate; as, to lie flat on the ground; hence, fallen; laid low; ruined; destroyed.
What ruins kingdoms, and lays cities flat! — Milton
I feel... my hopes all flat. — 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. — Shakespeare
6.
Lacking liveliness of commercial exchange and dealings; depressed; dull; as, the market is flat.
7.
Clear; unmistakable; peremptory; absolute; positive; downright.
Flat burglary as ever was committed. — Shakespeare
A great tobacco taker too, -- that's flat. — Marston
8.
(a) (Music) Below the true pitch; hence, as applied to intervals, minor, or lower by a half step; as, a flat seventh; A flat.
(b)
(Music) Not sharp or shrill; not acute; as, a flat sound.
9.
(Phonetics) Sonant; vocal; -- applied to any one of the sonant or vocal consonants, as distinguished from a nonsonant (or sharp) consonant.
10.
(Golf) Having a head at a very obtuse angle to the shaft; -- said of a club.
11.
(Grammar) Not having an inflectional ending or sign, as a noun used as an adjective, or an adjective as an adverb, without the addition of a formative suffix, or an infinitive without the sign to. Many flat adverbs, as in run fast, buy cheap, are from Anglo-Saxon adverbs in -e, the loss of this ending having made them like the adjectives. Some having forms in ly, such as exceeding, wonderful, true, are now archaic.
12.
(Horticulture) Flattening at the ends; -- said of certain fruits.
Of all who fell by saber or by shot, Not one fell half so flat as Walter Scott. — Lord Erskine

Some flat hoisting ropes, as for mining shafts, are made by sewing together a number of ropes, making a wide, flat band

Flat , adverb

1.
In a flat manner; directly; flatly.
Sin is flat opposite to the Almighty. — Herbert
2.
(Stock Exchange) Without allowance for accrued interest. [Broker's Cant]

Flat , noun

1.
A level surface, without elevation, relief, or prominences; an extended plain; specifically, in the United States, a level tract along the along the banks of a river; as, the Mohawk Flats.
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. — Shakespeare
3.
(Railroad Machinery) Something broad and flat in form
(a)
(Railroad Machinery) A flat-bottomed boat, without keel, and of small draught.
(b)
(Railroad Machinery) A straw hat, broad-brimmed and low-crowned.
(c)
(Railroad Machinery) A car without a roof, the body of which is a platform without sides; a platform car.
(d)
(Railroad Machinery) A platform on wheel, upon which emblematic designs, etc., are carried in processions.
4.
The flat part, or side, of anything; as, the broad side of a blade, as distinguished from its edge.
5.
(Architecture) A floor, loft, or story in a building;
(Architecture) a floor of a house, which forms a complete residence in itself; an apartment taking up a whole floor. In this latter sense, the usage is more common in British English.
6.
(Mining) A horizontal vein or ore deposit auxiliary to a main vein; also, any horizontal portion of a vein not elsewhere horizontal. — Raymond
7.
A dull fellow; a simpleton; a numskull. [Colloquial]
Or if you can not make a speech, Because you are a flat. — Holmes
8.
(Music) A character [♭] before a note, indicating a tone which is a half step or semitone lower.
9.
(Geometry) A homaloid space or extension.

Flat , transitive verb

1.
To make flat; to flatten; to level.
2.
To render dull, insipid, or spiritless; to depress.
Passions are allayed, appetites are flatted. — Barrow
3.
To depress in tone, as a musical note; especially, to lower in pitch by half a tone.

Flat , intransitive verb

1.
To become flat, or flattened; to sink or fall to an even surface. — Sir W. Temple
2.
(Music) To fall form the pitch.
Collocations (1)
To flat out , to fail from a promising beginning; to make a bad ending; to disappoint expectations. [Colloquial]