avoid 一般用于由于合同无效而撤销的情形，合同自始就是无效的；

cancel 一般用于由于当事人违反合同约定而使合同解除的情形，合同解除后将不追究其效力，例如在租船合同中，出租人的船舶未能在指定日期到达指定港口，承租人有权解除合同（经查元照英美法词典）；

terminate一般用于由于合同履行完毕或合同到期而终止的情形。terminate一般用于由于合同履行完毕或合同到期而终止的情形。

例句一

An avoided contract or a rescinded contract has no legal restraint from the time when it is concluded.

无效的合同或者被撤销的合同自始没有法律约束力。

例句二

本条所称月工资是指劳动者在劳动合同解除或者终止前十二个月的平均工资。

Monthly salary as mentioned in this Article means the average monthly salary of the worker for the 12 months before the cancellation or termination of the labor contract thereof.

例句三

在本合同终止时，卖方应当退还根据本合同从买方收到的所有预付金。

In the event of such termination of this Contract, Seller shall return to Buyer any advance payment received from Buyer under this Contract.