The Collaborative International Dictionary of English v.0.48:

Sergeant \Ser"geant\, n. [F. sergent, fr. L. serviens, -entis,
   p. pr. of servire to serve. See Serve, and cf. Servant.]
   [Written also serjeant. Both spellings are authorized. In
   England serjeant is usually preferred, except for military
   officers. In the United States sergeant is common for civil
   officers also.]
   1. Formerly, in England, an officer nearly answering to the
      more modern bailiff of the hundred; also, an officer whose
      duty was to attend on the king, and on the lord high
      steward in court, to arrest traitors and other offenders.
      He is now called sergeant-at-arms, and two of these
      officers, by allowance of the sovereign, attend on the
      houses of Parliament (one for each house) to execute their
      commands, and another attends the Court Chancery.
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            The sergeant of the town of Rome them sought.
                                                  --Chaucer.
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            The magistrates sent the serjeant, saying, Let those
            men go.                               --Acts xvi.
                                                  35.
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            This fell sergeant, Death,
            Is strict in his arrest.              --Shak.
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   2. (Mil.) In a company, battery, or troop, a noncommissioned
      officer next in rank above a corporal, whose duty is to
      instruct recruits in discipline, to form the ranks, etc.
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   Note: In the United States service, besides the sergeants
         belonging to the companies there are, in each regiment,
         a sergeant major, who is the chief noncommissioned
         officer, and has important duties as the assistant to
         the adjutant; a quartermaster sergeant, who assists the
         quartermaster; a color sergeant, who carries the
         colors; and a commissary sergeant, who assists in the
         care and distribution of the stores. Ordnance sergeants
         have charge of the ammunition at military posts.
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   3. (Law) A lawyer of the highest rank, answering to the
      doctor of the civil law; -- called also serjeant at law.
      [Eng.] --Blackstone.
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   4. A title sometimes given to the servants of the sovereign;
      as, sergeant surgeon, that is, a servant, or attendant,
      surgeon. [Eng.]
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   5. (Zool.) The cobia.
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   Drill sergeant. (Mil.) See under Drill.

   Sergeant-at-arms, an officer of a legislative body, or of a
      deliberative or judicial assembly, who executes commands
      in preserving order and arresting offenders. See
      Sergeant, 1.

   Sergeant major.
      (a) (Mil.) See the Note under def. 2, above.
      (b) (Zool.) The cow pilot.
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The Collaborative International Dictionary of English v.0.48:

Serjeant \Ser"jeant\, Serjeantcy \Ser"jeant*cy\, etc.
   See Sergeant, Sergeantcy, etc.
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   Serjeant-at-arms. See Sergeant-at-arms, under Sergeant.
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WordNet (r) 3.0 (2006):

serjeant
    n 1: an English barrister of the highest rank [syn: serjeant-
         at-law, serjeant, sergeant-at-law, sergeant]