nặng mặt 
make (pull, put on, wear) a long face [ nặng ] : (1) heavy, weighty, serious, ponderous; (2) low-constricted tone
[ mặt ] : (1) right; (2) face, surface, dial; (3) side, aspect
Most Common Compounds Set 1:
Most Common Compounds Set 2 :
nặng mặt make (pull, put on, wear) a long face