The Collaborative International Dictionary of English v.0.48:

Stringent \Strin"gent\ (str[i^]n"jent), a. [L. stringens,
   -entis, p. pr. of stringere to draw or bind tight. See
   Strain.]
   Binding strongly; making strict requirements; restrictive;
   rigid; severe; as, stringent rules.
   [1913 Webster]

         They must be subject to a sharper penal code, and to a
         more stringent code of procedure.        --Macaulay.
   [1913 Webster] -- Strin"gent*ly, adv. -- Strin"gent*ness,
   n.
   [1913 Webster]

WordNet (r) 3.0 (2006):

stringent
    adj 1: demanding strict attention to rules and procedures;
           "rigorous discipline"; "tight security"; "stringent
           safety measures" [syn: rigorous, stringent, tight]

Moby Thesaurus II by Grady Ward, 1.0:

60 Moby Thesaurus words for "stringent":
   Spartan, Spartanic, acid, acidulous, acrid, acrimonious,
   astringent, austere, authoritarian, binding, biting, bitter, bleak,
   caustic, confining, cutting, demanding, double-edged, dour,
   draconian, drawing, edged, escharotic, exacting, exigent, fierce,
   grim, hard, harsh, incisive, inclement, ironhanded, keen,
   meticulous, mordacious, mordant, penetrating, piercing, poignant,
   rigorist, rigorous, rough, rugged, scathing, severe, sharp,
   stabbing, stern, stinging, strict, strident, tart, tough,
   trenchant, ungentle, unsparing, vehement, violent, virulent,
   vitriolic