na-adjective
making light of; disregarding; treating as trivial
Used in negative contexts to express that something should not be taken lightly or neglected. Often appears in set phrases like あだやおろそかにできない or あだやおろそかには扱えない.
この問題はあだやおろそかにできない。
This problem cannot be taken lightly.
彼の警告をあだやおろそかにしてはいけない。
You must not disregard his warning.
The expression combines あだ (futility, transience) and おろそか (neglect, carelessness). The exact historical derivation is uncertain, but it likely developed as an emphatic phrase meaning 'to treat as both futile and negligible'.