The Collaborative International Dictionary of English v.0.48:

Irreprovable \Ir`re*prov"a*ble\, a.
   Incapable of being justly reproved; irreproachable;
   blameless; upright. -- Ir`re*prov"a*ble*ness, n. --
   Ir`re*prov"a*bly, adv.
   [1913 Webster]