Establish a usage, tradition, or standard to be followed in the future. For example, He set a precedent by having the chaplain lead the academic procession. The word precedent here signifies a previous instance or legal decision upon which future instances are based, a usage dating from the early 1400s. In British and American law it more specifically refers to a legal decision that may be used as a standard in subsequent cases.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.