Merciful post-war PM (7)
I believe the answer is:
clement
This clue is a double definition.
'merciful' is the first definition.
(similar in meaning)
'post-war pm' is the second definition.
(Clement Attlee, UK prime minister 1945-1951)
(Other definitions for clement that I've seen before include "gentle approach" , "nice" , "chap" , "Pope once" , "(Of weather) mild, lenient" .)