Decency is basic honest, polite behaviour towards other people. Not heroism — the ordinary minimum.
The phrase common decency is where the word does most of its work, since appealing to it claims that something is obvious rather than arguable. There is a second sense about propriety, and public decency is a legal category concerning behaviour in view of others. The phrase having the decency to do something is a reproach dressed as a compliment. The adjective decent covers both, and in British speech it also just means quite good.
1noundecencyHonest and considerate behaviour towards others.
“He might at least have had the decency to ring.”
Latin
decentia
English, today
decency
From Latin decentia, from decens. Equivalent to decent + cy. Compare French décence.
Etymology from Wiktionary, CC BY-SA