Noun
The wife or the widow of a marquis; a woman who has the rank and dignity of a marquis.
Source: Webster's dictionaryA woman with the rank of a marquess, or the wife of a marquess, is called a marchioness main citation in Great Britain and Ireland or a marquise main elsewhere in Europe. Source: Internet
From marquise, which means not only a marchioness but also an awning. Source: Internet
Anne is also called "marchioness". Source: Internet