If you know someone whose husband or wife has died, you can describe that person as widowed. The widowed lady next door may have lost her husband many years ago.
A man whose spouse has died is typically called a widower, while a woman is a widow. Both men and women can be described with the adjective widowed if their partners are no longer alive. These words come from a root that's shared by the Sanskrit vidhuh, which means "lonely or solitary," and the Latin viduus, "bereft or void."