ngọc trai thiên nhiên 
natural pearl [ ngọc ] : precious stone, gem; beautiful, precious, regal
[ trai ] : (1) [=giai] male; (2) to fast; (3) oyster; (4) study room
[ thiên ] : (1) thousand; (2) partial (to), favorable, pro-(something); (3) heaven, sky, God, heavenly, divine, celestial; (4) (classifier for articles, novels, chapters); (5) to move, shift, change; (6) section, part, piece
Most Common Compounds Set 1:
Most Common Compounds Set 2 :