unreasonableness; absurdity; irrationality
Refers to something that goes against reason or logic; often used in formal or critical contexts.
His argument is unreasonable.
Everyone opposed the absurdity of that rule.
理不尽 implies unfairness or unreasonableness that causes frustration, often in personal situations, whereas 不道理 is more abstract and formal.
Compound of 不 (fu, 'not') and 道理 (dōri, 'reason, logic'). The exact historical derivation is uncertain, but the word follows a common Sino-Japanese pattern for negating abstract nouns.