1.Definition: (of a musical note) lowered in pitch by one chromatic semitone
2.Definition: commercially inactive
"Flat sales for the month", "Prices remained flat", "A flat market"
3.Definition: flattened laterally along the whole length (e.g., certain leafstalks or flatfishes)
4.Definition: having a relatively broad surface in relation to depth or thickness
"Flat computer monitors"
5.Definition: having a surface without slope, tilt in which no part is higher or lower than another
"A flat desk", "Skirts sewn with fine flat seams"
6.Definition: having lost effervescence
"Flat beer", "A flat cola"
7.Definition: horizontally level
"A flat roof"
8.Definition: lacking contrast or shading between tones
9.Definition: lacking stimulating characteristics; uninteresting
"A flat joke"
10.Definition: lacking taste or flavor or tang
11.Definition: lacking the expected range or depth; not designed to give an illusion or depth
"A flat two-dimensional painting"
12.Definition: not modified or restricted by reservations
"A flat refusal"
13.Definition: not reflecting light; not glossy
"Flat wall paint"
14.Definition: sounded or spoken in a tone unvarying in pitch
15.Definition: stretched out and lying at full length along the ground
"Found himself lying flat on the floor"