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Webster 1913 Edition

adv.

In an irreverent manner.

adv.

Without due regard to the authority and character of the Supreme being; in an irreverent manner.

Without due respect to superiors.

irreverently ‎(comparative more irreverently, superlative most irreverently)

in an irreverent manner

irreverently in The Century Dictionary, The Century Co., New York, 1911
irreverently in Webster’s Revised Unabridged Dictionary, G. & C. Merriam, 1913