One-sided book spreading ideas (6)
I believe the answer is:
biased
'one-sided' is the definition.
(synonyms)
'book spreading ideas' is the wordplay.
'book' becomes 'b' (abbreviation for book).
'spreading' is an anagram indicator.
'ideas' is an anagram of 'iased'.
'b'+'iased'='BIASED'
(Other definitions for biased that I've seen before include "Having prejudice" , "Not impartial" , "favouring a particular idea" , "Prejudiced or partisan" , "Prejudiced or influenced in favour or against" .)