Stop holiday being cancelled (5,3)
I believe the answer is:
leave off
'stop' is the definition.
(I know that leave off is a more specific form of the action discontinue)
'holiday being cancelled' is the wordplay.
'holiday' becomes 'leave' (I've seen this before).
'being cancelled' becomes 'off' (similar in meaning).
'leave'+'off'='LEAVE OFF'
(Other definitions for leave off that I've seen before include "Cease, or shed garment" , "Give over!" , "not eating or drinking" .)