noun
A woman whose husband has died and who has not remarried. Neutral term, though in modern Japanese 未亡人 (みぼうじん) is also common.
彼女は若くして後家になった。
She became a widow at a young age.
未亡人 is a more formal or literary term for 'widow', often used in official contexts. 後家 is more everyday and can carry a slightly old-fashioned or colloquial feel.
The kanji 後 (after, later) and 家 (house, family) combine to mean 'the one left behind in the household', i.e., a widow. The exact historical derivation is uncertain, but the spelling is conventionally associated with this meaning.