The Collaborative International Dictionary of English v.0.48:

Strictness \Strict"ness\, n.
   Quality or state of being strict.
   [1913 Webster]

WordNet (r) 3.0 (2006):

strictness
    n 1: conscientious attention to rules and details [syn:
         strictness, stringency]
    2: uncompromising resolution [syn: sternness, strictness]

Moby Thesaurus II by Grady Ward, 1.0:

133 Moby Thesaurus words for "strictness":
   Sabbatarianism, absoluteness, accommodation, accord, accordance,
   accuracy, acquiescence, adaptation, adaption, adjustment,
   agreement, attention to detail, attention to fact, bibliolatry,
   bigotry, care for truth, censoriousness, choosiness,
   circumstantiality, closeness, compliance, confinement, conformance,
   conformation other-direction, conformity, congruity,
   conscientiousness, consistency, conventionality, correctness,
   correspondence, criticality, criticalness, crowdedness, delicacy,
   detail, discriminatingness, discrimination, discriminativeness,
   dogmatism, evangelicalism, exactingness, exactitude, exactness,
   exquisiteness, faithfulness, fastidiousness, faultlessness,
   fidelity, fineness, finicality, finicalness, finickiness,
   finickingness, flawlessness, flexibility, fundamentalism,
   fussiness, hair, hairbreadth, hairsbreadth, harmony, hideboundness,
   hyperorthodoxy, incapaciousness, incommodiousness, keeping,
   limitation, line, literalism, literality, literalness,
   malleability, mathematical precision, meticulousness, minuteness,
   narrow gauge, narrowness, nearness, niceness, nicety, obedience,
   observance, orthodoxy, particularity, particularness, perfection,
   perfectionism, pliancy, preciseness, precisianism, precision,
   priggishness, prudishness, punctilio, punctiliousness, punctuality,
   purism, puritanicalness, puritanism, reconcilement, reconciliation,
   refinement, restrictedness, restriction, right, rightness,
   rigidity, rigidness, rigor, rigorousness, sabbatism, scripturalism,
   scrupulosity, scrupulousness, selectiveness, selectivity,
   sensitivity, severity, slenderness, staunchness, stiff-neckedness,
   straitlacedness, straitness, strict interpretation, subtlety,
   taste, textualism, the letter, tight squeeze, tightness,
   traditionalism, uniformity