The Collaborative International Dictionary of English v.0.48:

Lenience \Le"ni*ence\ (l[=e]"n[i^]*ens or l[=e]n"yens; 106),
Leniency \Le"ni*en*cy\ (l[=e]"n[i^]*en*s[y^] or
   l[=e]n"yen*s[y^]), n.
   The quality or state of being lenient; lenity; clemency.
   [1913 Webster]

WordNet (r) 3.0 (2006):

leniency
    n 1: mercifulness as a consequence of being lenient or tolerant
         [syn: lenience, leniency, mildness, lenity]
    2: a disposition to yield to the wishes of someone; "too much
       indulgence spoils a child" [syn: indulgence, lenience,
       leniency]
    3: lightening a penalty or excusing from a chore by judges or
       parents or teachers [syn: lenience, leniency]

Moby Thesaurus II by Grady Ward, 1.0:

146 Moby Thesaurus words for "leniency":
   abatement, acceptance, accommodatingness, agreeableness, allayment,
   alleviation, assuagement, attentiveness, benevolence, blunting,
   calming, carelessness, charitableness, charity, clemency,
   commiseration, compassion, complaisance, concern, condolence,
   condonation, considerateness, consideration, damping, deadening,
   delicacy, demulsion, diminution, downiness, dulcification, dulling,
   easiness, easing, easygoingness, endurance, falling-off, favor,
   featheriness, feeling, flossiness, fluffiness, forbearance,
   forbearing, forbearingness, forgiveness, fortitude, generousness,
   gentleness, grace, heedfulness, helpfulness, humanity, hushing,
   impotence, imprecision, indifference, indulgence, insolidity,
   kindness, laxity, laxness, lenience, lenity, lessening, letdown,
   letup, lightening, long-sufferance, long-suffering, longanimity,
   looseness, loosening, lulling, magnanimity, mellowness,
   mercifulness, mercy, mindfulness, mitigation, modulation,
   mollification, morbidezza, negligence, nonresistiveness,
   nonrigidity, obligingness, overindulgence, overpermissiveness,
   pacification, palliation, pardon, pathos, patience,
   patience of Job, patientness, permissiveness, perseverance, pity,
   plushiness, pulpiness, quarter, quietening, quieting, reduction,
   regard, regardfulness, relaxation, relaxedness, relief, remission,
   remissness, reprieve, ruth, satininess, self-control, self-pity,
   silkiness, slackening, slackness, sloppiness, softening, softness,
   solicitousness, solicitude, soothing, sponginess, stoicism,
   subduement, sufferance, sweet reasonableness, sympathy, tact,
   tactfulness, tempering, tenderness, thought, thoughtfulness,
   tolerance, toleration, tranquilization, unrestraint, unsolidity,
   velvetiness, waiting game, waiting it out, weakness