modifier
noun [ C ] language specialized uk/ˈmɒd.ɪ.faɪ.ər/ us/ˈmɑː.də.faɪ.ɚ/
修饰语，限定语
a word or phrase that is used with another word or phrase to limit or add to its meaning
In "safety barrier" the noun "safety" is being used as a modifier. 在 safety barrier 中，名词 safety 被用作修饰语。