legal wife; legitimate wife
Refers to a man's officially recognized wife, as opposed to a concubine or mistress. The term is somewhat formal and may appear in historical or legal contexts.
He had a concubine in addition to his legal wife.
The kanji 嫡 means 'legitimate' or 'direct descent', and 妻 means 'wife'. The reading ちゃくさい is the on'yomi of the characters. The term is of Chinese origin and was used in historical Japanese legal and family systems.