The Collaborative International Dictionary of English v.0.48:

Lenient \Le"ni*ent\ (l[=e]"n[i^]*ent or l[=e]n"yent), a. [L.
   leniens, -entis, p. pr. of lenire to soften, fr. lenis soft,
   mild. Cf. Lithe.]
   [1913 Webster]
   1. Relaxing; emollient; softening; assuasive; -- sometimes
      followed by of. "Lenient of grief." --Milton.
      [1913 Webster]

            O?? relax the fibers, are lenient, balsamic.
                                                  --Arbuthnot.
      [1913 Webster]

            Time, that on all things lays his lenient hand.
                                                  --Pope.
      [1913 Webster]

   2. Mild; clement; merciful; not rigorous or severe; as, a
      lenient disposition; a lenient judge or sentence.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lenient \Le"ni*ent\, n. (Med.)
   A lenitive; an emollient.
   [1913 Webster]

WordNet (r) 3.0 (2006):

lenient
    adj 1: tolerant or lenient; "indulgent parents risk spoiling
           their children"; "too soft on the children"; "they are
           soft on crime" [syn: indulgent, lenient, soft]
    2: not strict; "an easy teacher"; "easy standards"; "lenient
       rules"; "an easy penalty"
    3: characterized by tolerance and mercy

Moby Thesaurus II by Grady Ward, 1.0:

95 Moby Thesaurus words for "lenient":
   Spartan, accepting, accommodating, accommodative, admissive,
   agreeable, allowing, armed with patience, attentive, balmy, bland,
   bleeding, careless, charitable, clement, commiserative,
   compassionate, complaisant, condolent, consenting, considerate,
   delicate, disciplined, easy, easygoing, endurant, enduring, faint,
   forbearant, forbearing, forgiving, generous, gentle, heedful,
   helpful, human, humane, impotent, imprecise, indifferent,
   indulgent, kind, kindly, lax, long-suffering, longanimous, loose,
   magnanimous, melting, merciful, mild, mindful, mindful of others,
   moderate, negligent, nonprohibitive, obliging, overindulgent,
   overpermissive, patient, patient as Job, permissive, permitting,
   persevering, philosophical, pitying, regardful, relaxed, remiss,
   ruthful, self-controlled, slack, slipshod, sloppy, smooth, soft,
   softhearted, solicitous, sparing, stoic, suffering, sympathetic,
   sympathizing, tactful, tender, tenderhearted, thoughtful, tolerant,
   tolerating, tolerative, understanding, unprohibitive, unrestrained,
   warmhearted, weak