Not at all certain (4)
I believe the answer is:
iffy
'not at all certain' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for iffy that I've seen before include "Dubious, risky (inf.)" , "Questionable - uncertain" , "Colloquially uncertain or doubtful" , "Unsure" , "Not to be trusted" .)