The Collaborative International Dictionary of English v.0.48:

Marquis \Mar"quis\, n. [F. marquis, OF. markis, marchis, LL.
   marchensis; of German origin; cf. G. mark bound, border,
   march, OHG. marcha. See March border, and cf.
   Marchioness, Marquee, Marquess.]
   A nobleman in England, France, and Germany, of a rank next
   below that of duke. Originally, the marquis was an officer
   whose duty was to guard the marches or frontiers of the
   kingdom. The office has ceased, and the name is now a mere
   title conferred by patent.
   [1913 Webster]

WordNet (r) 3.0 (2006):

Marquis
    n 1: humorist who wrote about the imaginary life of cockroaches
         (1878-1937) [syn: Marquis, Don Marquis, Donald Robert
         Perry Marquis]
    2: nobleman (in various countries) ranking above a count [syn:
       marquis, marquess]

Moby Thesaurus II by Grady Ward, 1.0:

39 Moby Thesaurus words for "marquis":
   Brahman, archduke, aristocrat, armiger, baron, baronet, blue blood,
   count, daimio, duke, earl, esquire, gentleman, grand duke, grandee,
   hidalgo, lace-curtain, laird, landgrave, lord, lordling, magnate,
   magnifico, margrave, noble, nobleman, optimate, palsgrave,
   patrician, peer, seigneur, seignior, silk-stocking, squire, swell,
   thoroughbred, upper-cruster, viscount, waldgrave