落空

làkòng
  1. to omit; to neglect (to do sth)
  2. to miss a chance; to let an opportunity slip by

CEDICT

疏忽而未顧及。

重編國語辭典

Homographs

落空 làokōng to fail to achieve something; to be fruitless
落空 luòkōng to fail; to fall through; to come to nothing

Entry Composition

1 落 là
  1. to leave out
  2. to be missing
  3. to leave behind or forget to bring
  4. to lag or fall behind
2 空 kòng
  1. to empty
  2. vacant
  3. unoccupied
  4. space
  5. leisure
  6. free time