na-adjective, noun
just; fair; proper; reasonable
Used for judgments, decisions, prices, or treatment that are fair and appropriate. Often appears in formal or written contexts.
裁判官は至当な判決を下した。
The judge handed down a fair verdict.
彼の要求は至当だと思う。
I think his demand is reasonable.
Compound of 至 (ultimate, most) and 当 (right, appropriate), literally 'most appropriate'. The exact historical derivation is uncertain, but the kanji combination conveys the meaning of supreme fairness.