The Collaborative International Dictionary of English v.0.48:

Venial \Ve"ni*al\, a. [OF. venial, F. v['e]niel, L. venialis,
   from venia forgiveness, pardon, grace, favor, kindness; akin
   to venerari to venerate. See Venerate.]
   1. Capable of being forgiven; not heinous; excusable;
      pardonable; as, a venial fault or transgression.
      [1913 Webster]

            So they do nothing, 't is a venial slip. --Shak.
      [1913 Webster]

   2. Allowed; permitted. [Obs.] "Permitting him the while
      venial discourse unblamed." --Milton.
      [1913 Webster]

   Venial sin (R. C. Theol.), a sin which weakens, but does
      not wholly destroy, sanctifying grace, as do mortal, or
      deadly, sins.
      [1913 Webster] -- Ve"ni*al*ly, adv. -- Ve"ni*al*ness,
      n. --Bp. Hall.
      [1913 Webster]

WordNet (r) 3.0 (2006):

venial
    adj 1: warranting only temporal punishment; "venial sin" [syn:
           minor, venial]
    2: easily excused or forgiven; "a venial error" [syn:
       excusable, forgivable, venial]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "venial":
   admissible, allowable, condonable, defensible, dispensable,
   excusable, exemptible, expiable, forgivable, harmless, inoffensive,
   insignificant, justifiable, legitimate, minor, pardonable, petty,
   reasonable, remissible, tolerable, tolerated, trifling, trivial,
   unimportant, unobjectionable, vindicable, warrantable