mortal sin
noun [ C usually singular ] uk/ˌmɔː.təl ˈsɪn/ us/ˌmɔːr.t̬əl ˈsɪn/
（天主教中的）弥天大罪
in the Roman Catholic religion, an action that is so bad that you will be punished for ever after your death if you do not ask God to forgive you
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