Verb flatten has 3 senses
  1. flatten - make flat or flatter; "flatten a road"; "flatten your stomach with these exercises"
    --1 is one way to
    shape, form
    Sample sentences:
    Somebody ----s something
    Something ----s something
  2. flatten, flatten out - become flat or flatter; "The landscape flattened"
    --2 is one way to change shape, change form, deform
    Sample sentence:
    Something ----s
  3. flatten, drop - lower the pitch of (musical notes)
    --3 is one way to change, alter, modify
    Antonyms: sharpen
    Sample sentence:
    Somebody ----s something