Source : Webster's Revised Unabridged Dictionary (1913)

Irreverent \Ir*rev"er*ent\, a. [L. irreverens, -entis: cf. F.
   irr['e]v['e]rent. See {In-} not, and {Reverent}.]
   Not reverent; showing a want of reverence; expressive of a
   want of veneration; as, an irreverent babbler; an irreverent
   jest.

Source : WordNet®

irreverent
     adj 1: showing lack of due respect or veneration; "irreverent
            scholars mocking sacred things"; "noisy irreverent
            tourists" [ant: {reverent}]
     2: characterized by a lightly pert and exuberant quality; "a
        certain irreverent gaiety and ease of manner" [syn: {impertinent},
         {pert}, {saucy}]
     3: not revering god [syn: {godless}]