Unreliable source (4)
I believe the answer is:
liar
'unreliable source' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for liar that I've seen before include "Fibber" , "one telling a story" , "One whose pants are on fire?" , "Teller of untruths" , "not straight [one]" .)