inexcusably

Adverb

• without any excuse
  • he is unjustifiably harsh on her
    

• in an unpardonable manner or to an unpardonable degree
  • he was inexcusably cruel to his wife
    

Related words

• Synonyms: 
  unjustifiably , unpardonably , unforgivably
• Antonyms: 
  justifiably , excusably , forgivably , pardonably