Improbable story (4,4)
I believe the answer is:
tall tale
'improbable story' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for tall tale that I've seen before include "unbelievable" , "Improbable story" , "Fanciful story" , "Incredible story" , "Story that is difficult to believe, lofty narrative" .)