不然

bùrán
  1. not so
  2. no
  3. or else
  4. otherwise
  5. if not
  6. How about ...?

CEDICT

Entry Composition

1 不 bù
  1. no; not so
  2. (bound form) not; un-
2 然 rán
  1. correct
  2. right
  3. so
  4. thus
  5. like this
  6. -ly