在英語中，契約一般稱為contract，協定一般稱為agreement。
何謂“contract”?
1999年中國《契約法》第二條對contract定義為： a contact in this law refers to an agreement establishing, modifying and terminating the civil rights and obligations between subjects of equal footing, that is, between natural persons, legal persons or other organizations”。根據這一定義，契約平等主體之間設立的確定民事權利和義務的協定。 ，
steven h. gifts編著的“law dictionary”中將contract 定義為“contract is a promise, or a set of promises, for breach of which the law gives remedy, or the performance of the which the law in some way recognize as a duty.”根據這一定義，契約是一種承諾，違反承諾可以得到法律救助，某種意義上法律將履行該承諾看做是一種補償。
l.b curzon 在其編撰的字典“a dictionary of law”給contract的定義：“contract is a legally binding agreement”根據這一定義，契約就是有法律約束力的協定。
綜合起來，有一個相同點，就是“contract is an agreement”，即可將契約說成是“an agreement which binds the parties concerned”或者說契約說成是“an agreement which is enforceable by law”， 也可以說：contracts are promises that the law will enforce。 ，
何謂“agreement”? ，
l.b “a consensus of mind, or evidence of such consensus, in spoke or written form, relating to anything done or to be done.”
根據這一定義，協定是對已經做或準備做的相關事宜，經過談判、協商後〉靡恢亂餳，以口頭或書面形式做出的約定?nbsp;
black "law dictionary"有兩個定義。一個是：“a concord of understanding and intention between two or more parties with respect to the effect upon their relative rights and duties, of certain past or future facts or performance”根據這一定義，協定即雙方或多方京某些過去或將來某些事實的相關權利、義務或相關權利、義務的履行而達成的一致理解和願望。
另一個是：“the consent of two or more persons concurring respecting the transmission of some property, right or benefits, with the view of contacting an obligation, a mutual obligation.”根據這一定義，協定即兩個或多個當事人，為了約定單方責任或相互責任，就財產權利、利益的轉移取得的一致同意。
contract(契約)和agreement(協定)是不是可以互換呢？
契約的成立必須具備幾個主要因素。它們（要約和承諾構成的）協定、約因、設立法律關係的願望和締約能力四大部分組成。
l.b curzon編著的“a diction of law”提到：“contract generally involves”
1. offer and absolute and unqualified acceptance (要約和絕對接受)
2. consensus ad idem (意思表示一致， 也叫meeting of minds)
3. intention to create legal relations (建立契約關係的意願)
4. genuineness of consent (同意的真實性)
5. contractual capacity of the parties (契約當事人的締約能力)
6. legality of object(標的物的合法性)
7. possibility of performance (履行的可能性)
8. certainty of terms(條款的確定性)
9. valuable consideration(等價有償)
black ’law dictionary" 中解釋道：although often used as synonyms with "contract", agreement is a broader term, e.g. an agreement might lack an essential element of a contact."
“契約任何一方當事人不得轉讓本契約”英文表述為“neither party hereto may assign this contract”，其中“hereto”表示“to the contract”，選用“neither party to the contract”較少。
3． 同義詞、近義詞、相關詞的序列
for value received，the undersigned does hereby sell, transfer, assign and set over to ______ all his right, tile and interest in and to a certain contract dated ______, 19____ by and between the undersigned and ______，a copy of which is annexed hereto.
在這裡的同義詞和近義詞並列（如sell, transfer, assign and set over，right和 tile and interest），在英文契約里十分普遍。這是出於嚴謹和杜絕漏洞的考慮，有的也屬於契約用語的固定模式。如：
this agreement is made and entered into by and between party a and party b.句中“made and entered into”和“by and between”兩組分別屬於同義詞和相關詞並列。
for and in consideration of mutual covenants and agreements contained herein, the parties hereby covenant and agree as follows: 句中“for and in consideration of ”， “covenants and agreements”三組同義司和近義詞並列。
the parties have agreed to vary the management on the terms and subject to the conditions contained herein. 這裡的“on the terms”和“subject to the conditions”是一個意思都表示“依照本協定的條款規定”。契約條款的固定模式是“terms and conditions”
再例如： ，
“party a wishes to be released and discharged from agreement as from the effective date”，一句中的“release”和“discharge”意思幾乎相同。
並列的詞還有：
ships and vessels
support and maintenance
licenses and permits
charges, fees, costs and expenses
any and all
any duties, obligations or liabilities
the partners, their heirs, successors and assigns
control and management of the partnership
applicable laws, regulations, decrees, directives, and rules
5. 拉丁詞 ，
在國外契約中，拉丁詞仍然是很常見：
比例稅率：用pro rate tax rate要比proportional tax rate多
從事慈善性服務的律師：pro bono lawyer，不怎么用lawyer engaged in charitable legal assistance
委託代理人：多用agent ad litem
contract 與 agreement的有無區別
在英語中，契約一般稱為contract，協定一般稱為agreement。
何謂“contract”?
1999年中國《契約法》第二條對contract定義為： a contact in this law refers to an agreement establishing, modifying and terminating the civil rights and obligations between subjects of equal footing, that is, between natural persons, legal persons or other organizations”。根據這一定義，契約平等主體之間設立的確定民事權利和義務的協定。 ，
steven h. gifts編著的“law dictionary”中將contract 定義為“contract is a promise, or a set of promises, for breach of which the law gives remedy, or the performance of the which the law in some way recognize as a duty.”根據這一定義，契約是一種承諾，違反承諾可以得到法律救助，某種意義上法律將履行該承諾看做是一種補償。
l.b curzon 在其編撰的字典“a dictionary of law”給contract的定義：“contract is a legally binding agreement”根據這一定義，契約就是有法律約束力的協定。
綜合起來，有一個相同點，就是“contract is an agreement”，即可將契約說成是“an agreement which binds the parties concerned”或者說契約說成是“an agreement which is enforceable by law”， 也可以說：contracts are promises that the law will enforce。 ，
何謂“agreement”? ，
l.b “a consensus of mind, or evidence of such consensus, in spoke or written form, relating to anything done or to be done.”
根據這一定義，協定是對已經做或準備做的相關事宜，經過談判、協商後〉靡恢亂餳，以口頭或書面形式做出的約定?nbsp;
black "law dictionary"有兩個定義。一個是：“a concord of understanding and intention between two or more parties with respect to the effect upon their relative rights and duties, of certain past or future facts or performance”根據這一定義，協定即雙方或多方京某些過去或將來某些事實的相關權利、義務或相關權利、義務的履行而達成的一致理解和願望。
另一個是：“the consent of two or more persons concurring respecting the transmission of some property, right or benefits, with the view of contacting an obligation, a mutual obligation.”根據這一定義，協定即兩個或多個當事人，為了約定單方責任或相互責任，就財產權利、利益的轉移取得的一致同意。
contract(契約)和agreement(協定)是不是可以互換呢？