What is a single word that means false accusation? [closed]

The word "libel" is one one the terms that can be used.

(OALD) the act of printing a statement about somebody that is not true and that gives people a bad opinion of them; the statement that is printed
♦ He sued the newspaper for libel.

More generally applicable is the word "calumny".

(OAld) [countable] a false statement about a person that is made to damage their reputation
♦ He accused the press of publishing vicious calumnies.