Make more interesting by adding details which may not be true (9)
I believe the answer is:
embellish
'make more interesting by adding details which may not be true' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for embellish that I've seen before include "He bills me so as to improve or decorate" , "Add false details" , "Make more attractive by adding ornament" , "Exaggerate" , "Add extra details to (story)" .)