The Collaborative International Dictionary of English v.0.48:

Irrespective \Ir`re*spec"tive\ ([i^]r`r[-e]*sp[e^]k"t[i^]v), a.
   1. Without regard for conditions, circumstances, or
      consequences; unbiased; independent; impartial; as, an
      irrespective judgment.
      [1913 Webster]

            According to this doctrine, it must be resolved
            wholly into the absolute, irrespective will of God.
                                                  --Rogers.
      [1913 Webster]

   2. Disrespectful. [Obs.] --Sir C. Cornwallis.
      [1913 Webster]

   Irrespective of, regardless of; without regard to; as,
      irrespective of differences.
      [1913 Webster]

WordNet (r) 3.0 (2006):

irrespective
    adv 1: in spite of everything; without regard to drawbacks; "he
           carried on regardless of the difficulties" [syn:
           regardless, irrespective, disregardless, no
           matter, disregarding]