Uncertain, doubtful (4)
I believe the answer is:
iffy
This clue is a double definition.
'uncertain' is the first definition.
(both can mean dubious)
'doubtful' is the second definition.
(I've seen this before)
(Other definitions for iffy that I've seen before include "Doubtful, not definite" , "Informally dubious or uncertain" , "Dodgy" , "Uncertain (colloq.)" , "Questionable - uncertain" .)