chain letter
noun [ C ] uk/ˈtʃeɪn ˌlet.ər/ us/ˈtʃeɪn ˌlet̬.ɚ/
连锁信（要求收信人复制数份再寄给其他人，有时还威胁如不照办会有厄运降临）
a letter sent to several people, who are each asked to send copies to several others, that sometimes threatens that bad things will happen if they do not send these copies