retainer
🇬🇧/rɪˈteɪnə(r)/ 🇺🇸/rɪˈteɪnər/A retainer is a fee that you pay to someone in order to make sure that they will be available to do work for you if you need them to. 预付聘金
noun [专属名词] 保持器;家臣;保持者;[机] 护圈;预付费用
I'll need a five-hundred-dollar retainer. 我将需要一笔500美元的预付聘金。