flatter; flattest
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.
Note: 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.
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]
11
of lighting conditions
: not producing strong shadows
a portrait taken in flat lighting
12
: not shiny
flat paint
13
British, of a battery
: no longer producing electricity : dead
The battery has gone flat. [=(US) the battery is dead; the battery has died]
plural flats
1
: a level area of land
—usually plural
salt flats
tidal flats
2
: a flat part or surface
the flat of your hand
the flat of a sword
3
a
: a musical note that is one semitone lower than a specified note
B flat
b
: a written symbol ♭ that is placed before a note to show that it should be played a semitone lower
4
US
: a shallow box in which young plants are grown
5
chiefly US
: a shoe or slipper that has a flat heel or no heel
—usually plural
She wore a casual dress and flats to the show.
6
chiefly British
: an apartment typically on one floor
They moved out of their old flat.
7
: a tire that does not have enough air
I drove over a nail and got a flat.
fix a flat
1
a
: on or against a flat surface
Lay the map flat on the desk.
b
: in the position of someone or something that is lying spread out on the ground or another surface
He slipped and landed/fell flat on his back/face.
2
: exactly or precisely
—used to describe something that happens quickly
He got there in two minutes flat.
in 10 seconds flat
She finished her homework in nothing flat. [=in no time at all; very quickly]
3
informal
: completely or absolutely
We asked for more time but they turned us down flat.
(US) If you ask me, what they're doing is flat wrong.
I'm flat broke. [=I have no money]
4
: below the correct musical pitch
He sang slightly flat.
Cite this Entry
“Flat.” Merriam-Webster.com Simple Definition, Merriam-Webster, https://www.merriam-webster.com/simple/flat. Accessed 17 Apr. 2026.
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