1.Definition: characterized by a lightly pert and exuberant quality

"A certain irreverent gaiety and ease of manner"

Related Adjective(s):impertinent, pert, saucy

2.Definition: not revering god

Related Adjective(s):godless

3.Definition: showing lack of due respect or veneration

"Irreverent scholars mocking sacred things", "Noisy irreverent tourists"