Refers to a man's wife after remarriage, often used in contrast to a first wife or in contexts of family lineage. Somewhat formal or literary.
After his first wife passed away, he took a second wife.
He has two children with his second wife.
Standard kanji spelling for 'second wife'.
Kana spelling is sometimes used for clarity or in informal writing.
Compound of 後 (のち, 'after') and 添い (そい, from 添う, 'to accompany'). Literally 'one who accompanies later', referring to a wife taken after a previous marriage.