愧疚 (kuì jiù) is a compound word expressing deep moral discomfort arising from having done something wrong or failed to fulfill a duty or expectation. The first character 愧 means 'to feel ashamed'—often tied to one’s own actions or perceived inadequacy—while 疚 means 'to feel remorseful' or 'to suffer inner pain', especially over harm caused to others. Together, they convey a stronger, more introspective and emotionally weighty sense of guilt than simpler terms like 罪 (guilt in a legal sense) or 害怕 (fear). It implies self-reproach, not just regret, and often involves empathy for those affected.

This word is commonly used in reflective, serious, or literary contexts—such as personal confessions, psychological descriptions, or moral discussions. It appears frequently in writing and formal speech but less often in casual conversation, where speakers might opt for milder phrases like 不好意思 (bù hǎo yìsi, 'sorry') or 对不起 (duì bu qǐ, 'I’m sorry'). 愧疚 carries an implicit assumption of responsibility and conscience, making it unsuitable for situations involving no personal fault or external blame.