1N-COUNT (封建社会的)封臣 In feudal society, a vassal was a man who gave military service to a lord, in return for which he was protected by the lord and received land to live on. (封建社会的)封臣
2N-COUNT [usually singular]附属国 If you say that one country is a vassal of another, you mean that it is controlled by it. 附属国 [written, disapproval]
Opponents of the treaty argue that monetary union will turn France into a vassal of Germany. [+ of]