adj. flat·ter, flat·test
1. Having a horizontal surface without a slope, tilt, or curvature.
2. Having a smooth, even, level surface: a skirt sewed with fine flat seams.
3. Having a relatively broad surface in relation to thickness or depth: a flat board. See Synonyms at level.
4. Stretched out or lying at full length along the ground; prone.
5. Free of qualification; absolute: a flat refusal.
6. Fixed; unvarying: a flat rate.
7. Lacking interest or excitement; dull: a flat scenario.
a. Lacking in flavor: a flat stew that needs salt.
b. Having lost effervescence or sparkle: flat beer.
a. Deflated. Used of a tire.
b. Electrically discharged. Used of a storage battery.
10. 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.
11. Commercially inactive; sluggish: flat sales for the month.
12. Unmodulated; monotonous: a flat voice.
13. Lacking variety in tint or shading; uniform: "The sky was bright but flat, the color of oyster shells" (Anne Tyler).
14. Not glossy; mat: flat paint.
a. Being below the correct pitch.
b. Being one half step lower than the corresponding natural key: the key of B flat.
16. Designating the vowel a as pronounced in bad or cat.
17. Nautical Taut. Used of a sail.
a. Level with the ground; horizontally.
b. On or up against a flat surface; at full length.
2. So as to be flat.
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.
1. A flat surface or part.
2. A stretch of level ground. Often used in the plural: 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.
a. A sign () used to indicate that a note is to be lowered by a half step.
b. A note that is lowered a half step.
11. Football The area of the field to either side of an offensive formation.
v. flat·ted, flat·ting, flats
1. To make flat; flatten.
2. Music To lower (a note) a semitone.
To sing or play below the proper pitch.
[Middle English, from Old Norse flatr; see plat- in Indo-European roots.]