The characters combine literally to mean “Ten Evils Not Pardoned”. This directly references a list of the ten most severe crimes in ancient Chinese law, for which even a general amnesty from the emperor would not apply.
The term 十恶不赦 is not just a strong adjective; it's a direct link to the legal and philosophical history of China. Its origin lies in the “Ten Abominations” (十恶), a list of capital offenses codified in the Tang Code (唐律) around the 7th century. These were crimes seen as so destructive to the cosmic and social order that they were unforgivable. The list included crimes like:
Comparison to Western Concepts: A useful Western parallel is the concept of “crimes against humanity” or “mortal sin” in Catholicism. However, a key difference highlights Chinese cultural values. The inclusion of crimes like “lack of filial piety” (不孝) on a list with treason and rebellion shows the immense importance of the Confucian family structure. In traditional Chinese thought, a crime against your own parents was as severe as a crime against the emperor, because a stable family was the foundation of a stable empire. 十恶不赦, therefore, condemns not just evil in a general sense, but evil that fundamentally threatens the pillars of Chinese society: the state and the family.
While its legal origins are ancient, 十恶不赦 is very much alive in modern Mandarin. It is a formal and extremely strong term.
Its connotation is always 100% negative and carries a heavy, serious tone.