inexcusable
adj. B2 Upper Intermediate US //ˌɪnɪkˈskjuzəbəɫ// UK //ˌɪnɛkskjˈuːsəbəl// in·ex·cus·able
adj. so bad or wrong that it is impossible to find a reason for it. You use this to describe a mistake or a behavior that is completely unacceptable.
adj. not able to be justified or defended; deserving of blame or punishment. Often used to describe actions or errors that are morally or socially indefensible.
It is inexcusable to arrive late to a funeral.
The manager found the employee's repeated failure to follow safety protocols completely inexcusable.
While the technical error was minor, the lack of a backup system was inexcusable for a company of that size and reputation.
From Middle French inexcusable, from Latin inexcusabilis.