madam

'I am sorry, madam, but the restaurant is fully booked for the evening,' said the waiter.

(Chinese) 服务员说：“对不起，女士，餐厅今晚已经订满了。”

The formal letter began with 'Dear Sir or Madam' because the sender did not know the recipient's name.

(Chinese) 这封正式信函以“尊敬的先生或女士”开头，因为发信人不知道收信人的姓名。