“经贸合作”翻译成economic and trade cooperation，为什么economic用的是adj.，而trade却用n.，为什么

第一，n可以修饰n。trade修饰cooperation，而为什么不用economy呢，理由就是楼下这位说的和economy经济实惠有歧义，为了不引起误解，所以用economic

第一这是个国际约定的专业词汇……就不多说了。
第二可以从逻辑上考虑中文的意思：“经贸“，这里主要是指有经济效应的贸易行为，换句话说“经”是用来形容“贸”的，因此用形容词也无可厚非。个人认为国外造这个词的时候可能也有此种考虑吧。

economic和trade都是用来修饰 cooperation的，名词和动词都可以修饰名词，这是习惯用语，所以就没有用economy

“经贸合作”翻译成economic and trade cooperation, 这是习惯用语.

economic is an adjective,

trade can be an adjective.

In dictionary, Definition of trade:

adjective
18.of or pertaining to trade or commerce.
19.used by, serving, or intended for a particular trade: trade journal.
20.Also, composed of, or serving the members of a trade: a trade club.

People use economic to avoid a second confused meaning of Economy: economy can be used as a synonym for efficiency (效率的代名词). Fuel economy measures how many miles per gallon a vehicle consumes. For this meaning, we use economical instead of economic as the adjective form.
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名词可以作定语修饰名词，作定语的 名词往往是说明其中名词的材料、用 途、时间、地点、内容、类别等。