flatten

Concise Oxford English Dictionary © 2008 Oxford University Press:
flatten/ˈflatn/

▶verb

• 1 make or become flat or flatter.

• 2 press (oneself) against a surface.

• 3 raze to the ground.

• 4 informal strike (someone) so as to make them fall down.

• 5 Music lower (a note) in pitch by a semitone.

– derivatives
flattened adjective,
flattener noun.