different between irremissible vs irremissibly

English

From Middle English irremyssible, from Old French irremissible, from Late Latin irremissibilis, from in- +? remissus +? -ibilis.

irremissible (comparative more irremissible, superlative most irremissible)

Not remissible.
Synonyms: unforgivable, unpardonable
Antonyms: forgivable, pardonable, remissible

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

irremissible +? -ly

irremissibly (comparative more irremissibly, superlative most irremissibly)

irremissibly in The Century Dictionary, New York, N.Y.: The Century Co., 1911.
Webster, Noah (1828) , “irremissibly”, in An American Dictionary of the English Language

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