A dowager is a serious-minded older woman, especially one who is a wealthy widow. In some countries, the widow of a king was historically known as the Queen dowager.
Dowager is an old-fashioned term of respect for a woman whose husband died and left her money and property, and often a title as well. The wife of a now-deceased count might have been known (and addressed) as a dowager countess, for example. In the old days, this title was useful since it distinguished a widow from the wife of the heir to her late husband's title. The heir's wife would be the duchess, while the widow would be the dowager duchess.