If or if not (7)
I believe the answer is:
whether
'if or if not' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for whether that I've seen before include "Conjunction indicating choice" , "If in fact" , "Whichever is the case" , "- - 'tis nobler in the mind... Shakespeare's 'Hamlet'" , "He threw (anag.)" .)