What is the translation express (adjective meaning fast) in Chinese?
'Express courier service' in Chinese is

速遞服務  or 快遞服務 

速遞/快遞 is shortened from '快速遞送/ 快速傳遞' (express delivery) . It can functions as an adjectival noun as in   速遞服務(express delivery service); 速遞文件(express delivery document)