Precedence pertains to ranking. A precedent is a previous example used to guide a decision.
The noun precedence pertains to ranking or status in order of importance or urgency.
The medics treated them in order of precedence according to their injuries.
The rules that govern the precedence of members of the Royal Family are complex.
The nounprecedent means an example from the past that provides evidence for an argument. It is most commonly used in legal circles and, more specifically, can be described as a previously decided case that guides the decision of a future case.
Having discovered a similar case in the past, the prosecution team used this precedent to support their argument.
There is precedent with last year's Smith versus Jones case.
Here are some common terms with precedent and precedence: