With nothing to lose, author uses complex reference book (9)
I believe the answer is:
thesaurus
'reference book' is the definition.
(thesaurus is a kind of reference book)
'with nothing to lose author uses complex' is the wordplay.
'with nothing' becomes 'o' (I've seen this in other clues).
'to lose' indicates named letters should be taken away.
'complex' indicates anagramming the letters.
'author'+'uses'='authoruses'
'authoruses' with 'o' taken out is 'authruses'.
'authruses' with letters rearranged gives 'THESAURUS'.
(Other definitions for thesaurus that I've seen before include "Wordy gathering" , "work we may refer to" , "Dictionary" , "lists?" , "storehouse" .)