The Collaborative International Dictionary of English v.0.48:

Baronet \Bar"on*et\, n. [Baron + -et.]
   A dignity or degree of honor next below a baron and above a
   knight, having precedency of all orders of knights except
   those of the Garter. It is the lowest degree of honor that is
   hereditary. The baronets are commoners.
   [1913 Webster]

   Note: The order was founded by James I. in 1611, and is given
         by patent. The word, however, in the sense of a lesser
         baron, was in use long before. "Baronets have the title
         of 'Sir' prefixed to their Christian names; their
         surnames being followed by their dignity, usually
         abbreviated Bart. Their wives are addressed as 'Lady'
         or 'Madam'. Their sons are possessed of no title beyond
         'Esquire.'" --Cussans.
         [1913 Webster]

WordNet (r) 3.0 (2006):

baronet
    n 1: a member of the British order of honor; ranks below a baron
         but above a knight; "since he was a baronet he had to be
         addressed as Sir Henry Jones, Bart." [syn: baronet,
         Bart]

Moby Thesaurus II by Grady Ward, 1.0:

57 Moby Thesaurus words for "baronet":
   Bayard, Brahman, Don Quixote, Gawain, Lancelot, Ritter, Sidney,
   Sir Galahad, archduke, aristocrat, armiger, bachelor, banneret,
   baron, blue blood, caballero, cavalier, chevalier, companion,
   count, daimio, duke, earl, esquire, gentleman, grand duke, grandee,
   hidalgo, knight, knight bachelor, knight banneret, knight baronet,
   knight-errant, lace-curtain, laird, landgrave, lord, lordling,
   magnate, magnifico, margrave, marquis, noble, nobleman, optimate,
   palsgrave, patrician, peer, seigneur, seignior, silk-stocking,
   squire, swell, thoroughbred, upper-cruster, viscount, waldgrave