Part of speech: Adjective (satellite)
failing in what duty requires
Example: derelict (or delinquent) in his duty; neglectful of his duties; remiss of you not to pay your bills
Remiss, Neglectful, Derelict, Delinquent
The word "remiss" comes from Latin remissus, which comes from Middle English remisse.
Many Latin words entered English twice—once through French and once through direct borrowing.