The Collaborative International Dictionary of English v.0.48:

Gannet \Gan"net\, n. [OE. gant, AS. ganet, ganot, a sea fowl, a
   fen duck; akin to D. gent gander, OHG. ganazzo. See Gander,
   Goose.] (Zool.)
   One of several species of sea birds of the genus Sula,
   allied to the pelicans.
   [1913 Webster]

   Note: The common gannet of Europe and America (Sula
         bassana), is also called solan goose, chandel
         goose, and gentleman. In Florida the wood ibis is
         commonly called gannet.
         [1913 Webster]

   Booby gannet. See Sula.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Gentleman \Gen"tle*man\, n.; pl. Gentlemen. [OE. gentilman
   nobleman; gentil noble + man man; cf. F. gentilhomme.]
   [1913 Webster]
   1. A man well born; one of good family; one above the
      condition of a yeoman.
      [1913 Webster]

   2. One of gentle or refined manners; a well-bred man.
      [1913 Webster]

   3. (Her.) One who bears arms, but has no title.
      [1913 Webster]

   4. The servant of a man of rank.
      [1913 Webster]

            The count's gentleman, one Cesario.   --Shak.
      [1913 Webster]

   5. A man, irrespective of condition; -- used esp. in the
      plural (= citizens; people), in addressing men in popular
      assemblies, etc.
      [1913 Webster]

   Note: In Great Britain, the term gentleman is applied in a
         limited sense to those having coats of arms, but who
         are without a title, and, in this sense, gentlemen hold
         a middle rank between the nobility and yeomanry. In a
         more extended sense, it includes every man above the
         rank of yeoman, comprehending the nobility. In the
         United States, the term is applied to men of education
         and good breeding of every occupation.
         [1913 Webster]

   Gentleman commoner, one of the highest class of commoners
      at the University of Oxford.

   Gentleman usher, one who ushers visitors into the presence
      of a sovereign, etc.

   Gentleman usher of the black rod, an usher belonging to the
      Order of the Garter, whose chief duty is to serve as
      official messenger of the House of Lords.

   Gentlemen-at-arms, a band of forty gentlemen who attend the
      sovereign on state occasions; formerly called gentlemen
      pensioners. [Eng.]
      [1913 Webster]

WordNet (r) 3.0 (2006):

gentleman
    n 1: a man of refinement
    2: a manservant who acts as a personal attendant to his
       employer; "Jeeves was Bertie Wooster's man" [syn: valet,
       valet de chambre, gentleman, gentleman's gentleman,
       man]

Moby Thesaurus II by Grady Ward, 1.0:

107 Moby Thesaurus words for "gentleman":
   Brahman, Brahmin, acceptable person, archduke, aristocrat, armiger,
   baron, baronet, bloke, blue blood, boy, buck, butler,
   capital fellow, chap, chauffeur, chevalier, coachman, count,
   daimio, diamond, driver, duke, earl, equerry, esquire, faithful,
   fellow, galantuomo, gardener, gee, gem, gent, gentilhomme, gillie,
   good fellow, good lot, good man, good person, good sort,
   good woman, grand duke, grandee, guy, he, hidalgo, him, his,
   hombre, homme, honest man, honest woman, houseboy, houseman, jewel,
   lace-curtain, lady, laird, landgrave, lord, lord-in-waiting,
   lordling, magnate, magnifico, male, male being, male person, man,
   man of honor, manservant, margrave, marquis, masculine, mensch,
   nob, noble, nobleman, optimate, palsgrave, patrician, pearl, peer,
   perfect gentleman, perfect lady, persona grata, prince, real lady,
   real man, right sort, rough diamond, seigneur, seignior,
   silk-stocking, squire, straight shooter, swell, thoroughbred,
   true blue, truepenny, trusty, upper-cruster, valet,
   valet de chambre, viscount, waldgrave, woman of honor, worthy



Bouvier's Law Dictionary, Revised 6th Ed (1856):

GENTLEMAN. In the English law, according to Sir Edward Coke, is one who
bears a coat of armor. 2 Inst. 667. In the United States, this word is
unknown to the law, but in many places it is applied, by courtesy, to all
men. See Poth. Proc. Crim. sect. 1, App. Sec. 3.