Barth, KarlPronunciation: /bɑːt, bɑːθ/Definition of Barth, Karl (1886–1968), Swiss Protestant theologian. His seminal work Epistle to the Romans (1919) established a neo-orthodox or theocentric approach to contemporary religious thought which remains influential on Protestant theology. Derivatives BarthianPronunciation: /ˈbɑːtɪən/ adjective Barth, Karl in other Oxford dictionaries Definition of Barth, Karl in the US English dictionary