An area of level ground, often used for horse racing, either as a general term or specifically referring to level horse-racing ground without jumps or the central area of a racecourse in australia.

(music) A note played a semitone lower than a natural, denoted by the symbol ♭ placed after the letter representing the note (e.g., B♭) or in front of the note symbol (e.g. ♭♪).

(informal, automotive) A flat tyre/flat tire.

(in the plural) A type of ladies' shoe with a very low heel.

(in the plural) A type of flat-soled running shoe without spikes.

(painting) A thin, broad brush used in oil and watercolour painting.

A term used in swordfighting to refer to the flat side of a blade, as well as the palm of the hand and adjacent part of the fingers.

A wide, shallow container or pallet.

(mail) A large mail piece measuring at least 8 1/2 by 11 inches, such as catalogs, magazines, and unfolded paper enclosed in large envelopes.

(rail transport, US) A railroad car without a roof, and whose body is a platform without sides; a platform car or flatcar.

A flat-bottomed boat, without keel, and of small draught.

(geometry) A subset of n-dimensional space that is congruent to a Euclidean space of lower dimension.

A straw hat, broad-brimmed and low-crowned.

A flat sheet for use on a bed.

(publishing) A flat, glossy children's book with few pages.

A platform on a wheel, upon which emblematic designs etc. are carried in processions.

(mining) A horizontal vein or ore deposit auxiliary to a main vein; also, any horizontal portion of a vein not elsewhere horizontal.

(technical, theatre, stagecraft) A rectangular wooden structure covered with masonite, lauan, or muslin, often produced in standard modules, that is used to build wall surfaces on stage. Flats can be painted and outfitted with doors and/or windows to depict a building or other part of a scene. It's a hard-surfaced alternative to a backcloth or backdrop.

(entomology) Any of various hesperiid butterflies that spread their wings open when they land.

(historical) An early kind of toy soldier having a flat design.

Short for flat ride (“spinning amusement ride”).

(optics) A flat (i.e. plane) mirror

(gambling, slang) A cheater's die with the edges shaved to make certain rolls more likely.

(poker slang) To make a flat call; to call without raising.

(intransitive) To become flat or flattened; to sink or fall to an even surface.

(intransitive, music, colloquial) To fall from the pitch.

(transitive, music) To depress in tone, as a musical note; especially, to lower in pitch by half a tone.

(transitive) To dash or throw

(intransitive) To dash, rush

A flat is something that has no variations in height, is in a horizontal line or plane, is smooth with no surface irregularities, and can also refer to having small or invisible breasts and/or buttocks.

Without variation in level, quantity, value, tone, etc., consistently depressed or lacklustre, fixed and unvarying in fees or fares, without variations in pitch in music or voice, and without variation in tone or hue in colors, appearing dull and not glossy.

(figurative) Lacking liveliness or action, depressed, uninteresting, dull and boring; lacking in depth, substance, or believability, underdeveloped, one-dimensional.

(music, note) Lowered by one semitone.

(music) Of a note or voice, lower in pitch than it should be.

Absolute; downright; peremptory.

(of a tire or other inflated object) Deflated, especially because of a puncture.

(of a carbonated drink) With all or most of its carbon dioxide having come out of solution so that the drink no longer fizzes or contains any bubbles.

(wine) Lacking acidity without being sweet.

(of a battery) Unable to emit power; dead.

(juggling, of a throw) Without spin; spinless.

(grammar) Not having an inflectional ending or sign, such 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".

(golf, of a golf club) Having a head at a very obtuse angle to the shaft.

(horticulture, of certain fruits) Flattening at the ends.

(of measurements of time) Exact.

So as to be flat.

Bluntly.

(of accurately measured timings) Exactly, precisely.

(with units of time, distance, etc) Used to emphasize the smallness of the measurement.

Completely.

Directly; flatly.

(finance, slang) Without allowance for accrued interest.