Source : Webster's Revised Unabridged Dictionary (1913)

Irreverence \Ir*rev"er*ence\, n. [L. irreverentia: cf. F.
   irr['e]v['e]rence.]
   The state or quality of being irreverent; want of proper
   reverence; disregard of the authority and character of a
   superior.

Source : WordNet®

irreverence
     n 1: an irreverent mental attitude [ant: {reverence}]
     2: a disrespectful act [syn: {violation}]