flat 1 
(flăt)
(flăt)adj. flat·ter, flat·test
1.
a. Having a smooth, even surface: a flat field. See Synonyms at level.
b. Having a relatively broad level surface in relation to thickness or depth: a flat box.
2.
a. Being in horizontal position; lying down: flat on his back.
b. Being without slope or curvature: a flat line on a chart.
c. Having a low heel or no heel: flat shoes.
3. Free of qualification; absolute: a flat refusal.
4. Fixed; unvarying: a flat rate.
5. Lacking interest or excitement; dull: a flat scenario.
6.
a. Lacking in flavor: a flat stew that needs salt.
b. Having lost effervescence or sparkle: flat beer.
7.
a. Deflated. Used of a tire.
b. Electrically discharged. Used of a storage battery.
8. Of or relating to a horizontal line that displays no ups or downs and signifies the absence of physiological activity: A flat electroencephalogram indicates a loss of brain function.
9. Of or relating to a hierarchy with relatively few tiers or levels: a flat organization chart.
10. Commercially inactive; sluggish: flat sales for the month.
11. Unmodulated; monotonous: a flat voice.
12. Lacking variety in tint or shading; uniform: "The sky was bright but flat, the color of oyster shells" (Anne Tyler).
13. Not glossy; matte: flat paint.
14. Music
a. Being below the correct pitch.
b. Being one half step lower than the corresponding natural key: the key of B flat.
15. Designating the vowel a as pronounced in bad or cat.
16. Nautical Taut. Used of a sail.
17. Informal Having small breasts.
adv.
1.
a. Level with the ground; horizontally.
b. On or up against a flat surface; at full length.
2. So as to be flat.
3.
a. Directly; completely: went flat against the rules; flat broke.
b. Exactly; precisely: arrived in six minutes flat.
4. Music Below the intended pitch.
5. Business Without interest charge.
n.
1. A flat surface or part.
2. often flats A stretch of level ground: salt flats.
3. A shallow frame or box for seeds or seedlings.
4. A movable section of stage scenery, usually consisting of a wooden frame and a decorated panel of wood or cloth.
5. A flatcar.
6. A deflated tire.
7. A shoe with a flat heel.
8. A large flat piece of mail.
9. A horse that competes in a flat race. Also called runner.
10. Music
a. A sign (♭) used to indicate that a note is to be lowered by a semitone.
b. A note that is lowered a semitone.
11. Football The area of the field to either side of an offensive formation.
v. flat·ted, flat·ting, flats
v.tr.
1. To make flat; flatten.
2. Music To lower (a note) a semitone.
v.intr.
Music
Music
To sing or play below the proper pitch.
[Middle English, from Old Norse flatr; see plat- in the Appendix of Indo-European roots.]
flatly adv.
flatness n.