Tim Bowen’s been working flat out to deliver this look at word grammar.
The word flat can function as a noun, adjective or adverb.
Apart from its use to mean ‘an apartment’, the noun can also be used to mean the flat part of something, as in ‘She hit the table with the flat of her hand’. If you have a flat, you have a puncture, especially in American English. A flat can also be used to denote a musical note that is one semitone lower than a particular note, as in ‘Can you play a flat here?’
The plural form flats can either mean shoes with no heels, as in ‘She’s wearing flats today’ or it can refer to a low flat area of land, usually wet land near a large area of water, as in ‘Building houses on the flats is a recipe for disaster’.
The adjectival form has numerous meanings, including its use to mean direct and definite, as in ‘a flat refusal’ and its use to describe a very low level of business activity, as in ‘January is always a flat month in the pub business’.
The adverb flat can refer to music or singing that is out of tune, as in ‘You’re singing flat. Can’t you at least try to keep in tune?’ It can also mean ‘exactly’, as in ‘She fell asleep in five seconds flat’. It can also mean ‘completely’, as in ‘They turned me down flat’ or ‘I would lend you some money but I’m flat broke at the moment’. If you work flat out, you work as quickly or with as much effort as possible, as in ‘The factory is working flat out to keep up with demand’.