đồng thời khi đó 
at that time, at the same time as, when [ đồng ] : (1) unit of currency, money; coin; (2) field; (3) same, co-, fellow; (4) copper, brass
[ thời ] : time(s), era
[ khi ] : occasion, time (when something happens), when, at the time of, if
[ đó ] : that, those, there, that
Most Common Compounds Set 1:
Most Common Compounds Set 2 :