Not British, Weimar dramatist is genuine (4)
I believe the answer is:
echt
'is genuine' is the definition.
(echt means genuine or authentic)
'not british weimar dramatist' is the wordplay.
'not' indicates named letters should be taken away.
'british' becomes 'br'.
'weimar dramatist' becomes 'Brecht' (Bertolt Brecht, playwright during Weimar Germany).
'brecht' with 'br' removed is 'ECHT'.
(Other definitions for echt that I've seen before include "Genuine (German)" , "Genuine - authentic" , "True" , "German's real" , "Genuine -- honest" .)