Where does “unexcusably” come from?
unexcusably (English) comes from English unexcusable, from English excusable, from Old French escusable, from Latin excusabilis, from Latin -bilis, from Proto-Italic -ðlis, from Proto-Indo-European -dʰlis, from Proto-Indo-European -dʰlom — Alternative form of *-trom; instrumental suffix;...
unexcusably (English): inexcusably
Ancestry of “unexcusably”, step by step