Books about a river long and variable of course (9)
I believe the answer is:
naturally
'of course' is the definition.
(synonyms)
'books about a river long and variable' is the wordplay.
I cannot really see how this works, but
'about' could be 'a' (abbreviation in Chambers) and 'a' is present in the answer.
'books' could be 'nt' (New Testament) and 'nt' is present in the leftover letters.
'a' is present in the answer.
'river' could be 'r' (abbreviation for river) and 'r' is present in the answer.
'long' could be 'l' and 'l' is located in the answer.
'variable' could be 'y' (algebra) and 'y' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for naturally that I've seen before include "as you might expect" , "Without affectation" , "As a matter of course" , "Unforced" , "as normal" .)