unless /ənˈles/ conj. 1. 如果不 (=if not): You will fail unless you work hard.如果你不努力工作，你就要失败。I will not go unless I hear from him. (=I will not go if I don’t hear from him.) 如果他不通知我,我就不去。 2.除非…(主句必须是否定句，从句可为省略句，直接跟形容词或分词连用)：We shall not call the meeting unless absolutely necessary. 除非绝对必要，否则我们将不召开会议。He will not come unless invited. 除非邀请，他才肯来。