mar·chio·ness 
(märshə-nĭs, mär′shə-nĕs)
(märshə-nĭs, mär′shə-nĕs)n.
1. The wife or widow of a marquess.
2. A noblewoman ranking above a countess and below a duchess. Also called marquise.
3. Used as a title for such a noblewoman.
[Medieval Latin marchiōnissa, wife of a margrave, marchioness, feminine of marchiō, marchiōn-, marquis, from marca, boundary, of Germanic origin; see merg- in the Appendix of Indo-European roots.]