To be remiss means to be careless or negligent about doing something you're supposed to do. If you're remiss in your duties, you're failing to handle your responsibilities properly.

A student would be remiss if they forgot to study for an important test they knew was coming. A babysitter would be remiss if they got distracted by their phone instead of watching the children in their care. A ship's captain would be remiss if they failed to check the weather forecast before setting sail.

The word often appears in the phrase “I would be remiss if I didn't...” which means “I would be failing in my responsibility if I didn't...” A teacher might say, “I would be remiss if I didn't remind you about the field trip permission slips due tomorrow.” This polite construction acknowledges an important duty that needs attention.

Being remiss is different from making an honest mistake. It suggests you should have known better or should have been more careful. When someone is remiss, they've neglected something they had a clear obligation to do. The word carries a tone of mild criticism: being remiss means falling short of what people reasonably expected of you.