Threat finale (2,4)
I believe the answer is:
or else
'threat finale' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for or else that I've seen before include "Statement that threatens" , "Do it . . . . . . - an informal warning" , "Threatening phrase" , "If not, then - vaguely threatening" , "Alternatively" .)