Squadron leader always cut off (5)
I believe the answer is:
sever
'cut off' is the definition.
(to sever is to cut)
'squadron leader always' is the wordplay.
'leader' suggests taking the first letters.
'always' becomes 'ever' (synonyms).
The first letter of 'squadron' is 's'.
's'+'ever'='SEVER'
(Other definitions for sever that I've seen before include "Detach" , "Cut off suddenly" , "Cleave" , "Cut right off" , "Divide, cut" .)