used to

used to 过去常常，曾经

【例句】

◆ The house we used to live in was a very old building．我们曾经居住过的那所房子是很旧的。  

◆ It used to be called the〝year off〞between school and university．中学和大学之间的时期过去常常被叫作”休年假”。（课标高考）