"inexcusably" in the adverb sense
1. inexcusably, unpardonably, unforgivably
in an unpardonable manner or to an unpardonable degree
"he was inexcusably cruel to his wife"
2. unjustifiably, inexcusably
without any excuse
"he is unjustifiably harsh on her"
Source: WordNet® (An amazing lexical database of English)
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