To make or become flat or flatter. She used a rolling pin to flatten the dough.
To knock down or demolish. The storm managed to flatten several trees in the park.
To press or squeeze something to make it level or even. He tried to flatten the creases in his shirt with his hands.
To reduce the intensity or impact of something. The new regulations are intended to flatten the curve of the virus spread.
To convert (a complex or hierarchical data structure) into a simpler, one-dimensional form. Before exporting the table, you need to flatten the nested JSON objects.
Music: to lower (a note) in pitch by a semitone. The arranger decided to flatten the third to give the chord a bluesy feel.