On no account (3,2,4,4)
I believe the answer is:
not on your life
'on no account' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for not on your life that I've seen before include "On no account whatsoever" , "Never! (colloq.)" , "Like someone else's autobiography" , "Expression of strong denial" , "Emphatically, no!" .)