unspokendeal

2. A secret arrangement between people who never put it in words.

There was an unspokendeal between the neighbors to keep the street quiet at night.

3. A rule that everyone follows without being told.

In our family, there is an unspokendeal that whoever cooks does not have to wash the dishes.

4. A quiet promise between two people who trust each other.

They had an unspokendeal to call each other every Sunday.