hệ điều hành 
operating system [ hệ ] : branch, system; generation
[ điều ] : (1) thing, matter, item; article (of penal code, constitution); (2) smoking pipe; (3) bird [=chim]
[ hành ] : (1) scallion, spring onion; (2) to act, execute, carry out; (3) stem; (4) to go, travel (on foot); (5) one of the five elements
Most Common Compounds Set 1:
Most Common Compounds Set 2 :