The Collaborative International Dictionary of English v.0.48:

Irreligious \Ir`re*li"gious\, a. [L. irreligiosus: cf. F.
   irr['e]ligieux.]
   [1913 Webster]
   1. Destitute of religion; not controlled by religious motives
      or principles; ungodly. Cf. Impious.
      [1913 Webster]

            Shame and reproach are generally the portion of the
            impious and irreligious.              --South.
      [1913 Webster]

   2. Indicating a lack of religion; profane; wicked; as,
      irreligious speech.
      [1913 Webster]

WordNet (r) 3.0 (2006):

irreligious
    adj 1: hostile or indifferent to religion [ant: religious]