noun
being directly concerned; matter in question; concerned party or matter
Refers to direct concern or involvement in the matter at issue. Practical learner usage is mainly in compounds such as 当事者, 'party concerned,' and 当事国, 'country directly concerned.'
当事者同士で冷静に話し合ってください。
Please discuss it calmly between the parties concerned.
その国は紛争の当事国ではない。
That country is not a party directly involved in the conflict.
Formal modifier meaning 'the relevant' or 'said'; it identifies what is being referred to but does not by itself mean direct involvement.
Sino-Japanese compound written with 当, associated with what is relevant or in question, and 事, 'matter' or 'affair.' This is a component explanation of the spelling rather than a precise historical derivation.