The Collaborative International Dictionary of English v.0.48:

Sheriff \Sher"iff\, n. [OE. shereve, AS. sc[imac]r-ger?fa;
   sc[imac]r a shire + ger?fa a reeve. See Shire, and Reeve,
   and cf. Shrievalty.]
   The chief officer of a shire or county, to whom is intrusted
   the execution of the laws, the serving of judicial writs and
   processes, and the preservation of the peace.
   [1913 Webster]

   Note: In England, sheriffs are appointed by the king. In the
         United States, sheriffs are elected by the legislature
         or by the citizens, or appointed and commissioned by
         the executive of the State. The office of sheriff in
         England is judicial and ministerial. In the United
         States, it is mainly ministerial. The sheriff, by
         himself or his deputies, executes civil and criminal
         process throughout the county, has charge of the jail
         and prisoners, attends courts, and keeps the peace. His
         judicial authority is generally confined to
         ascertaining damages on writs of inquiry and the like.
         Sheriff, in Scotland, called sheriff depute, is
         properly a judge, having also certain ministerial
         powers. Sheriff clerk is the clerk of the Sheriff's
         Court in Scotland. Sheriff's Court in London is a
         tribunal having cognizance of certain personal actions
         in that city. --Wharton, Tomlins. Erskine.
         [1913 Webster] Sheriffship
         Sheriffry
         Sheriffdom
         Sheriffalty

WordNet (r) 3.0 (2006):

sheriff
    n 1: the principal law-enforcement officer in a county

Moby Thesaurus II by Grady Ward, 1.0:

47 Moby Thesaurus words for "sheriff":
   G-man, MP, bailiff, beadle, beagle, bound bailiff, captain,
   catchpole, chief of police, commissioner, constable, deputy,
   deputy sheriff, detective, fed, federal, flic, gendarme,
   government man, inspector, lictor, lieutenant, mace-bearer,
   marshal, mounted policeman, narc, officer, patrolman,
   peace officer, police captain, police commissioner,
   police constable, police inspector, police matron, police officer,
   police sergeant, policeman, policewoman, portreeve, reeve,
   roundsman, sergeant, sergeant at arms, superintendent, tipstaff,
   tipstaves, trooper



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

SHERIFF. The name of the chief officer of the county. In Latin he is called
vice comes, because in England he represented the comes or earl. His name is
said to be derived from the Saxon seyre, shire or county, and reve, keeper,
bailiff, or guardian.
     2. The general duties of the sheriff are, 1st. To keep the peace within
the county; he may apprehend, and commit to prison all persons who break the
peace or attempt to break it, and bind any one in a recognizance to keep the
peace. He is required ex officio, to pursue and take all traitors,
murderers, felons and rioters. He has the keeping of the county gaol and he
is bound to defend it against all attacks. He may command the posse
comitatus. (q.v.)
     3.-2d. In his ministerial capacity, the sheriff is bound to execute
within his county or bailiwick, all process issuing from the courts of the
commonwealth.
     4.-3d. The sheriff also possesses a judicial capacity, but this is very
much circumscribed to what it was at common law in England. It is now
generally confined to ascertain damages on writs of inquiry and the like.
     5. Generally speaking the sheriff has no authority out of his county. 2
Rolle's Rep. 163; Plowd, 37 a. He may, however, do mere ministerial acts out
of his county, as making a return. Dalt. Sh. 22. Vide, generally, the
various Digests and Abridgments, h.t.; Dalt. Sher.; Wats. Off. and Duty of
Sheriff; Wood's Inst. 75; 18 Eng. Com. Law Rep. 177; 2 Phil. Ev. 213; Chit.
Pr. Index, h.t.; Chit. Pr. Law, Index, h.t.



The Devil's Dictionary (1881-1906):

SHERIFF, n.  In America the chief executive office of a country, whose
most characteristic duties, in some of the Western and Southern
States, are the catching and hanging of rogues.

    John Elmer Pettibone Cajee
    (I write of him with little glee)
    Was just as bad as he could be.

    'Twas frequently remarked:  "I swon!
    The sun has never looked upon
    So bad a man as Neighbor John."

    A sinner through and through, he had
    This added fault:  it made him mad
    To know another man was bad.

    In such a case he thought it right
    To rise at any hour of night
    And quench that wicked person's light.

    Despite the town's entreaties, he
    Would hale him to the nearest tree
    And leave him swinging wide and free.

    Or sometimes, if the humor came,
    A luckless wight's reluctant frame
    Was given to the cheerful flame.

    While it was turning nice and brown,
    All unconcerned John met the frown
    Of that austere and righteous town.

    "How sad," his neighbors said, "that he
    So scornful of the law should be --
    An anar c, h, i, s, t."

    (That is the way that they preferred
    To utter the abhorrent word,
    So strong the aversion that it stirred.)

    "Resolved," they said, continuing,
    "That Badman John must cease this thing
    Of having his unlawful fling.

    "Now, by these sacred relics" -- here
    Each man had out a souvenir
    Got at a lynching yesteryear --

    "By these we swear he shall forsake
    His ways, nor cause our hearts to ache
    By sins of rope and torch and stake.

    "We'll tie his red right hand until
    He'll have small freedom to fulfil
    The mandates of his lawless will."

    So, in convention then and there,
    They named him Sheriff.  The affair
    Was opened, it is said, with prayer.
                                                     J. Milton Sloluck