了然於胸 liǎo rán yú xiōng

DEFINITIONS

  1. to be well aware of sth
  2. to understand clearly

CHARACTERS

了 liǎo to finish; particle of completed action
然 rán yes, certainly; pledge, promise
於 yú in, at, on; interjection alas!
胸 xiōng breast, bosom, chest; thorax