1. having a smooth, level surface without raised areas
2. having little or no height; not thick
3. lacking energy, enthusiasm, or interest

1. an apartment on one floor of a building
Usage: British
2. a tire that has lost air pressure

1. in a flat manner; completely

Examples

• The table has a flat surface perfect for writing.
• She lives in a small flat in London.
• The tire went flat on the highway.
• His performance was flat and uninspiring.
• The box is flat enough to fit under the bed.
• She gave him a flat refusal.
• The singer sang flat during the entire song.