vô cùng bí mật 
ultrasecret [ vô ] : (1) in-, im-, (negative prefix); (2) in, at, on; (3) to go into, enter [= vào]
[ cùng ] : same, together; to act together (with), and; to follow
[ bí ] : (1) pumpkin, squash; (2) fine-toothed; (3) secret, mysterious; (4) obstructed, constipated, blocked, stumped
[ mật ] : (1) honey, molasses; (2) gall, bile; (3) secret, confidential, classified; (4) dense, thick, close, intimate
Most Common Compounds Set 1:
Most Common Compounds Set 2 :