The Collaborative International Dictionary of English v.0.48:

Sutler \Sut"ler\, n. [D. zoetelaar, OD. soetelaar, a small
   trader, especially in camps, fr. soetelen to undertake low
   offices; cf. G. sudeln to do dirty work, to sully, soil, E.
   suds.]
   A person who follows an army, and sells to the troops
   provisions, liquors, and the like.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sutler
    n 1: a supplier of victuals or supplies to an army [syn:
         sutler, victualer, victualler, provisioner]

Moby Thesaurus II by Grady Ward, 1.0:

20 Moby Thesaurus words for "sutler":
   caterer, chandler, commissariat, commissary, donor, furnisher,
   manciple, merchant, patron, provider, provisioner, purveyor,
   quartermaster, retailer, steward, stock clerk, storekeeper,
   supplier, victualer, vivandier



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

SUTLER. A man whose employment is to sell provisions and liquor to a camp.
     2. By the articles of war, art. 29, no sutler is permitted to sell any
kind of liquor or victuals, or to keep his house or shop open for the
entertainment of soldiers, after nine at night, or before the beating of the
reveillee, or upon Sundays during divine service or sermon, on penalty of
being dismissed all future sutling. And by art. 60, all sutlers are to be
subject to orders according to the rules and discipline of war.