The Chinese idiom '十恶不赦' is formed by directly combining the characters '十' (ten), '恶' (evils/crimes), '不' (not), and '赦' (pardon). It originates from the historical legal concept of the 'Ten Abominations' in imperial Chinese law, which were ten specific grave offenses considered so heinous that they were excluded from any pardon or amnesty, thus yielding the literal meaning of 'ten evils not pardonable' and denoting utterly unforgivable crimes.