Deliberate exaggeration (9)
I believe the answer is:
hyperbole
'deliberate exaggeration' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for hyperbole that I've seen before include "Exaggerated claims" , "not to be taken literally" , "Deliberate exaggeration used for effect" , "The use of exaggeration for effect" , "Exaggerated language, not meant literally" .)