noun
Refers to a woman who becomes a wife after a previous marriage has ended, typically through divorce or death. The term is somewhat old-fashioned and may carry a slightly negative or pitiable nuance in modern usage.
彼女は二度添いとして、前の妻の子供たちともうまくやっていかねばならなかった。
As a second wife, she had to get along with the children from the previous marriage.
継母 specifically means stepmother, focusing on the relationship with the children, whereas 二度添い emphasizes the marital status of being a second wife.
Composed of 二度 (twice, second time) and 添い (from 添う, to accompany or become a spouse). The exact historical derivation is uncertain, but it literally means 'second accompanying' and has been used to refer to a second wife.