The Collaborative International Dictionary of English v.0.48:

Yeoman \Yeo"man\, n.; pl. Yeomen. [OE. yoman, [yogh]eman,
   [yogh]oman; of uncertain origin; perhaps the first, syllable
   is akin to OFries. g[=a] district, region, G. gau, OHG. gewi,
   gouwi, Goth. gawi. [root]100.]
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   1. A common man, or one of the commonly of the first or most
      respectable class; a freeholder; a man free born.
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   Note: A yeoman in England is considered as next in order to
         the gentry. The word is little used in the United
         States, unless as a title in law proceedings and
         instruments, designating occupation, and this only in
         particular States.
         [1913 Webster]

   2. A servant; a retainer. [Obs.]
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            A yeman hadde he and servants no mo.  --Chaucer.
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   3. A yeoman of the guard; also, a member of the yeomanry
      cavalry. [Eng.]
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   4. (Naut.) An interior officer under the boatswain, gunner,
      or carpenters, charged with the stowage, account, and
      distribution of the stores.
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   Yeoman of the guard, one of the bodyguard of the English
      sovereign, consisting of the hundred yeomen, armed with
      partisans, and habited in the costume of the sixteenth
      century. They are members of the royal household.
      [1913 Webster]

WordNet (r) 3.0 (2006):

yeoman of the guard
    n 1: officer in the (ceremonial) bodyguard of the British
         monarch [syn: yeoman, yeoman of the guard, beefeater]