Remiss means careless in doing what you were supposed to do. Remiss of me, remiss in his duty, it would be remiss not to.
It appears almost entirely in two polite formulas: it would be remiss of me not to, said before saying a thank you, and remiss in his duty, said in a report. It is formal, and nobody uses it about anything trivial.
1adjectiveremissCareless in doing what you were supposed to do.
“The inspector found the manager remiss in checking the fire alarms.”
remiss is a quality.
re-MISS → you MISSed what was yours to do
You missed what you were meant to do, and you have no excuse ready.
hooks ontomiss
Latin remissus means slack or negligent, from remittere, to let go — re, back, plus mittere, to send.
Latin
remissus — languid, negligent
Middle English
remisse
English, today
remiss
Built from
From Middle English remisse, remysse, from Latin remissus (“languid, negligent”), perfect passive participle of remittō (“remit”).
Etymology from Wiktionary, CC BY-SA