horizontal; not sloping; level

broad and smooth, without raised or hollow areas

having a broad surface and little thickness

a flat case

shallow

a flat dish

said of shoes: without a raised heel

said of shoe heels: low

definite and unmistakable

a flat refusal

fixed or absolute

charge a flat rate

lacking animation; dull or monotonous

Trade is a bit flat

said of a sparkling drink: having lost effervescence

said of a tyre: lacking air; deflated

said of a battery: having lost its charge

said of a musical note: lowered a semitone in pitch

said of a key: having one or more flats in the signature

lower than the proper musical pitch

uniform in colour

said of a painting or photograph: lacking contrast or depth

an area of level ground; a plain

mudflats

a musical note one semitone lower than a specified or particular note

the character (♭) indicating this

on or against a flat surface

Keep your feet flat on the ground

so as to be spread out; at full length

lie flat

fall flat on the ground

with the broad surfaces, as distinct from the edges, facing up and down

lay the tiles flat

wholly; completely

flat broke

absolutely and emphatically

turn an offer down flat