Ward off disaster at last during a check (5)
I believe the answer is:
avert
'ward off' is the definition.
('avert' can be a synonym of 'ward off')
'disaster at last during a check' is the wordplay.
'at last' says to take the final letters.
'during' indicates putting letters inside.
'check' becomes 'vet' (I've seen this before**).
The last letter of 'disaster' is 'r'.
'a'+'vet'='avet'
'r' placed within 'avet' is 'AVERT'.
(Other definitions for avert that I've seen before include "Turn aside, prevent" , "Avoid" , "use preventive measures" , "Turn away from, say gaze" , "Turn away, prevent" .)