1 : having a smooth, level, or even surface : not having curves or bumps
▪ flat ground ▪ the flat top of the table ▪ the flat landscape of the prairie ▪ a flat stomach ▪ a flat wall 2 : having a wide, smooth surface and little thickness
▪ Coins are usually round and flat. ▪ small, flat computer disks ▪ a flat piece of wood 3 of a shoe heel : very low and wide
▪ flat heels ; also of a shoe : having a flat heel or no heel
▪ wearing flat shoes 4 : spread out on or along a surface
▪ The soldiers were lying flat on the ground. ▪ He was (lying) flat on his back. 5 : very clear and definite : absolute
▪ a flat refusal ▪ His comments were a flat contradiction of his sister's statement. ◊In British English the expression and that's flat! is used to stress that a statement or decision is definite and will not be changed.
▪ I'm not going to do it and that's flat! [=and that's that] 6 a : not changing in amount
▪ They charged a flat rate for their services. ▪ a flat [=fixed] fee ▪ Ticket sales have been/remained flat. [=have not increased or decreased] ▪ flat profits ▪ a flat tax [=a tax that is paid at the same rate by everyone]
b : not having much business activity
▪ The market is very flat for this time of year. 7 : not having much interest or energy : dull
▪ flat writing ▪ a flat performance ▪ He spoke in a flat, tired voice. 8 of a drink : no longer having bubbles
▪ This beer is flat. = This beer has gone flat. ▪ flat ginger ale ▪ flat champagne 9 of a tire : not having enough air
▪ I got a flat tire from a nail in the street. ▪ The tire was (slightly) flat. 10 music a : lower than the true pitch
▪ Her singing was slightly flat.
b : lower than a specified note by a semitone
▪ B flat [=a note that is a semitone lower than B] — compare ¹natural 8, ¹sharp 13 11 of lighting conditions : not producing strong shadows
▪ a portrait taken in flat lighting 12 : not shiny
▪ flat paint 13 Brit, of a battery : no longer producing electricity : dead
▪ The battery has gone flat. [=(US) the battery is dead; the battery has died]