Wiktionary
n. An unspoken rule.
Usage examples of "unwritten rule".
The unwritten rule is that whoever has the can or is cooking up has first go, and the rest has to be shared.
We had ridden out on Buck, but I had left him at the foot of the hill, there being an unwritten rule against letting mules or tamed lopers walk on graves.
Another unwritten rule was that the depredations should cease by 2200 hours.
Feeling used and grossly unappreciated, I had broken the unwritten rule and quit the I.
It is an unwritten rule that cadets at the top five percent of the class usually are assured—.
Since we'd been together, we sort of had an unwritten rule about feeding….
It was as if there was an unwritten rule in the coffee shop that you didn’.
The law library was open, no appointments were necessary, but the unwritten rule was that you should at least ask one of the Brethren before using their books.