Open Voltaire's work — don't close it (6)
I believe the answer is:
candid
'open' is the definition.
(I know that open can be written as candid)
'voltaire's work don't close it' is the wordplay.
'voltaire's work' becomes 'Candide' (1759 work by Voltaire).
'don't close it' means to remove the last letter (the letter which closes the word is removed).
'candide' with its last letter taken away is 'CANDID'.
(Other definitions for candid that I've seen before include "Honest and open about what one thinks" , "Frank, honest" , "Forthrightly sincere" , "Frank and outspoken" , "'Forthright, open (6)'" .)