Толковый словарь английского языка - flatten

verb (~ed; ~ing) Date: 1630 transitive verb to make flat: as, to make level or smooth, to knock down, to make dull or uninspired, to make (as paint) lusterless, to stabilize especially at a lower level, intransitive verb to become flat or flatter: as, to become dull or spiritless, to extend in or into a flat position or form, to become uniform or stabilized often at a new lower level, ~er noun