The state of being flat / The state of being two-dimensional; planar : planarity / The state of being bland : dullness

plural of flatness

simple past tense and past participle of flat

In a horizontal line or plane; not sloping. / Smooth; having no protrusions, indentations or other surface irregularities, or relatively so. / (slang) Having small or invisible breasts and/or buttocks.

(transitive, obsolete) To beat or strike; pound / (transitive) To dash or throw / (intransitive) To dash, rush

(in the phrase 'the flat') Level ground in general.

(chiefly Britain, New England, New Zealand and Australia, archaic elsewhere) An apartment, usually on one level and usually consisting of more than one room.

So as to be flat. / Bluntly. / (of accurately measured timings) Exactly, precisely. / (with units of time, distance, etc) Used to emphasize the smallness of the measurement. / Completely.

(poker slang) To make a flat call; to call without raising. / (intransitive) To become flat or flattened; to sink or fall to an even surface. / (intransitive, music, colloquial) To fall from the pitch.

(music) A tone one semitone below A, between G and A, denoted A♭. / (music) A key or other mechanism for producing an A-flat. / (music) The key of A-flat major.