1. Having been made flat or flatter
   "The flattened surface was ideal for the experiment";
   - planate

1. Make flat or flatter
   "flatten a road";
   - pancake
    
2. Become flat or flatter
   "The landscape flattened";
   - flatten out, pancake
    
3. Destroy or completely remove a building or structure
   "When a force occupies an enemy fortress, it may flatten the fortifications";
   - level, raze, rase [archaic], dismantle, tear down, take down, pull down, demolish, knock down
    
4. (music) lower the pitch of (musical notes)
   "The singer flattened the high notes to stay in her comfortable range";
   - drop

See also: planar, two-dimensional

Type of: alter, change, change form, change shape, deform, destroy, destruct, form, modify, shape, spifflicate [Brit, informal], spiflicate [Brit, informal], uncreate [literary]

Encyclopedia: Flatten, Moselle