1 : to appeal to as furnishing authority or motive
2 : to put into legal effect or call for the observance of
: enforce [invoking his Fifth Amendment privilege]
3 : to introduce or put into operation [invoking economic sanctions]
4 : to be the cause of [the…decision invoked the final hardship "U.S. Code "]
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.