precedent (n.)

early 15c., "previous instance or circumstance which may be taken as a rule in subsequent similar cases; a custom, habit, or rule established," from the adjective precedent "preceding in time, previous, former" (c. 1400), from Old French precedent (also used as a noun) and directly from Latin praecedentum (nominative praecedens), present participle of praecedere "go before" (see precede).

Meaning "thing or person that goes before another" is attested from mid-15c. Specifically in law, "a judicial decision which serves as a rule for future determinations in similar or analogous cases," by 1680s. As a verb meaning "to furnish with a precedent" from 1610s, now only in past participle precedented.