Unscrupulously accusing people of disloyalty (as by saying they were Communists)

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
1950, with -ism + name of U.S. Sen. Joseph R. McCarthy (1908-1957), leader of U.S. anti-Communist agitation. The term is said to have been coined by "Washington Post" political cartoonist Herbert Block ("Herblock"). The surname is from Irish Mac Carthaigh ...

Wikipedia Word definitions in Wikipedia
McCarthyism is the practice of making accusations of subversion or treason without proper regard for evidence. It also means "the practice of making unfair allegations or using unfair investigative techniques, especially in order to restrict dissent or ...

The Collaborative International Dictionary Word definitions in The Collaborative International Dictionary
McCarthyism \McCarthyism\ prop. n. [from Senator Joseph McCarthy, who repeatedly asserted without evidence that numerous communists were present in the United States government.] Unscrupulously accusing people of disloyalty (as by saying they were Communists). ...