Definition of Forswear
In criminal law, to make oath to that which the deponent knows to be untrue. This term is wider in its scope than "perjury,” for the latter, as a technical term, includes the idea of the oath being taken before a competent court or officer, and relating to a material issue, which is not implied by the word "forswear.” See Perjury.
That's the definition of Forswear in Black's Law Dictionary 6th Edition. Courtesy of Cekhukum.com.