Radical cleaner after books about liberalism (9)
I believe the answer is:
tolerance
'liberalism' is the definition.
(thesaurus)
'radical cleaner after books about' is the wordplay.
'radical' is an anagram indicator.
'after' says to put letters next to each other.
'books' becomes 'ot' (Old Testament).
'about' says the letters should be written backwards.
'ot' backwards is 'to'.
'cleaner' is an anagram of 'lerance'.
'lerance' after 'to' is 'TOLERANCE'.
(Other definitions for tolerance that I've seen before include "Ability to endure pain" , "example of permissiveness" , "ecumenical spirit?" , "Willingness to accept the beliefs of others" , "Allowable variation (in size)" .)