To set a precedent is to do something that later cases will be measured against. The first time is now the rule, whether anybody meant it to be.
It takes for: that ruling sets a precedent for every case after it. The phrase is legal at root and has spread everywhere else, and it nearly always arrives as a warning — you hear it from the person who does not want the thing done. Without precedent means it has never happened; a dangerous precedent is what an objector calls the one they lost.
1phraseset a precedentTo do something that later cases will follow.
“That ruling will set a precedent for every case after it.”
set a precedent is a first case that later ones follow.
Practised in Common Word Pairs