The Collaborative International Dictionary of English v.0.48:

Lustral \Lus"tral\, a. [L. lustralis, fr. lustrum: cf. F.
   lustral. See Lustrum.]
   1. Of or pertaining to, or used for, purification; as,
      lustral days; lustral water.
      [1913 Webster]

   2. Of or pertaining to a lustrum.
      [1913 Webster]

Moby Thesaurus II by Grady Ward, 1.0:

40 Moby Thesaurus words for "lustral":
   abstergent, apologetic, ascetic, atoning, cathartic, cleaning,
   cleansing, compensational, compensatory, depurative, detergent,
   diuretic, emetic, expiatory, expurgatory, lustrational, lustrative,
   penitential, piacular, propitiatory, purgative, purgatorial,
   purging, purificatory, purifying, reclamatory, recompensing,
   redeeming, redemptive, redressing, reparative, reparatory,
   repentant, repenting, restitutional, restitutive, restitutory,
   righting, satisfactional, squaring