的确，两个单词都可用作指合同或契约期限的延续，但两者意思虽然相近，却有较大差异。

两者的主要差别在于renewal是指重新创制一种法律关系或用一新合同取代旧合同，而非仅仅延展先前的关系或合同(the re-creation of a legal relationship or the replacement of an old contract with a new contract，as opposed to the mere extension of a previous relationship of contract *Black's Law Dictionary, 7th edition, at p. 1299, West Group (1999).)，故其为合同或契约等的“重订”或“续订”而非旧合同或契约的“展期” (先前不少英汉词典不加区别的将renewal of a contract或to renew a contract译为合同的“展期”显然是错误的)。

如：

If the operator fails to improve upon warning, apart from non-renewal of contract after completion, the HD also has the ultimate right to reenter the premises and terminate the tenancy, and remove the operator from the approved list of operators qualified for future tenders. 

若警告无效，房屋署除可选择不与有关承包商 续订合同外， 亦有权实时终止承包合约， 收 回街市， 并将有关承包商从认可承包商名册中除名， 使其不能获判未来的街市承包合约。 

而extension则指同一合同或契约延续一定规定期间的效力（the continuation of the same contract for a specified period *Black's Law Dictionary, 7th edition，at p. 604，West Group)，故其才真正是合同或契约等的“展期”。

同理，与renewal和extension相对应的动词renew及extend与合同或契约等连用时也应各自区别，分另译为合同的“续签”及合同的“展期”。

如：

Personal data (relating to employment in and appointments to the public service) including those relating to recruitment, renewal and extension of contracts, variation of conditions of service, promotion, discipline and integrity checking. 

个人资料(与公共服务的聘用及委任有关)，包括与招聘、续签合约及将合约展期、更改僱用 条款、晋升、纪律事宜及操守审查有关的资料。