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.
As a second wife, she had to get along with the children from the previous marriage.
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.