Definition of flat :
1. A car without a roof, the body of which is a platform without sides; a platform car.
2. A character  before a note, indicating a tone which is a half step or semitone lower.
3. A dull fellow; a simpleton; a numskull.
4. A flat- bottomed boat, without keel, and of small draught.
5. A floor, loft, or story in a building; especially, a floor of a house, which forms a complete residence in itself.
6. A homaloid space or extension.
7. A horizontal vein or ore deposit auxiliary to a main vein; also, any horizontal portion of a vein not elsewhere horizontal.
8. 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.
9. 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.
10. A platform on wheel, upon which emblematic designs, etc., are carried in processions.
11. A straw hat, broad- brimmed and low- crowned.
12. Below the true pitch; hence, as applied to intervals, minor, or lower by a half step; as, a flat seventh; A flat.
13. Clear; unmistakable; peremptory; absolute; positive; downright.
14. Flattening at the ends; - said of certain fruits.
15. Having a head at a very obtuse angle to the shaft; - said of a club.
16. Having an even and horizontal surface, or nearly so, without prominences or depressions; level without inclination; plane.
17. In a flat manner; directly; flatly.
18. Lacking liveliness of commercial exchange and dealings; depressed; dull; as, the market is flat.
19. 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.
20. 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 AS. 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.
21. Not sharp or shrill; not acute; as, a flat sound.
22. Something broad and flat in form
23. Sonant; vocal; - applied to any one of the sonant or vocal consonants, as distinguished from a nonsonant ( or sharp) consonant.
24. Tasteless; stale; vapid; insipid; dead; as, fruit or drink flat to the taste.
25. The flat part, or side, of anything; as, the broad side of a blade, as distinguished from its edge.
26. To become flat, or flattened; to sink or fall to an even surface.
27. To depress in tone, as a musical note; especially, to lower in pitch by half a tone.
28. To fall form the pitch.
29. To make flat; to flatten; to level.
30. To render dull, insipid, or spiritless; to depress.
31. Unanimated; dull; uninteresting; without point or spirit; monotonous; as, a flat speech or composition.
32. Wanting relief; destitute of variety; without points of prominence and striking interest.
33. Without allowance for accrued interest.
thin, downright, tight, unconditioned, crashing, supine, monotonic, tied, positive, direct, straightaway, unpleated, light, extended, politic, utter, unshaded, multidimensional, big, savourless, lying down, flattened, colors, monotone, suave, aseptic, flavourless, matt, unerect, flatten, punctured, drab, unrelieved, straight off, instantly, unlimited, pure, unleavened, arrant, pedestrian, prone, fallen, directly, arid, limited, out-and-out, unbounded, humdrum, compressed, unfolded, firm, muddy, solid, perfect, flat tire, thoroughgoing, excite, prosaic, colorless, change, unmitigated, now, damned, recumbent, uninspired, categoric, two-dimensional, sterile, earthbound, regressive, unreserved, thorough, consummate, immediately, lusterless, all-out, unseasoned, unstimulating, dim, unwavering, unexciting, fixed, dry, prostrate, flat-out, matte, at once, like a shot, underdeveloped, matter-of-fact, raised, lackluster, plane, sheer, unraised, right away, matted, complete, lifeless, deflated, rough, flatcar, stodgy, total, flatbed, straighten, decumbent, spiritless, taste, unimaginative, procumbent, forthwith, murky, mat, set, noneffervescent, blooming
continuous (part of speech: adjective)
incessant, un-intermittent, continuing, interminable, undying, consistent, unvarying, endless, monolithic, monotonous, undeviating, indefatigable, ceaseless, unchangeable, regular, everlasting, robot-like, continual, constant, perennial, cyclical, sequential, consecutive, repeated, unbroken, recurrent, homogeneous, unchanging, continuous, repetitive, straight, lasting, connected, invariable, perpetual, unceasing, featureless, persistent, seamless, unremitting, gapless, uniform, habitual, coherent, steady, nonstop, unending
non-resonant (part of speech: adjective)
flat (part of speech: adjective)
low (part of speech: adjective)
smooth (part of speech: adjective)
lacquered, smooth, even, satin-smooth, polished, slippery, glossy, frictionless, slilken, burnished, sleek, satiny, silky, edgeless, velvety, streamlined, slick, varnished, shiny, glazed, glassy, slithery, marble
apartments (part of speech: noun)
categorical (part of speech: adjective)
tasteless (part of speech: adjective)
- He turned for a moment to look out across the Flat at the city. - "Warlord of Kor", Terry Gene Carr.
- If the lathe bed is provided with ways having a flat surface, as was shown in Fig. - "Modern Machine-Shop Practice, Volumes I and II", Joshua Rose.
- What a jolly flat you have there! - "The Jolliest School of All", Angela Brazil.