noun
immorality; corruption; moral lapse
Refers to a violation of moral principles, often with a nuance of betraying one's own conscience or societal ethics. Used in serious or literary contexts.
彼は背徳の生活に溺れた。
He indulged in a life of immorality.
その行為は背徳と見なされた。
The act was regarded as a moral lapse.
不道徳 is a more common, everyday word for 'immoral' or 'unethical', while 背徳 carries a heavier, often literary nuance of betraying one's own moral standards.
堕落 emphasizes a fall into depravity or degradation, often with a sense of personal decline, whereas 背徳 focuses on the violation of moral principles itself.
From Middle Chinese 背德 (puʌiH tək̚), literally 'turn one's back on virtue'. The kanji 背 means 'back' or 'to go against', and 徳 means 'virtue' or 'morality'.