high crime n: a crime of infamous nature contrary to public morality but not technically constituting a felony
: an offense that the U.S. Senate deems to constitute an adequate ground for removal of the president, vice president, or any civil officer as a person unfit to hold public office and deserving of impeachment
Source: Merriam-Webster's Dictionary of Law ©1996. Merriam-Webster, Incorporated. Published under license with Merriam-Webster, Incorporated.