A long way to rise in the air force (3)
I believe the answer is:
far
'a long way' is the definition.
(I've seen this before)
'rise in the air force' is the wordplay.
'rise' is a reversal indicator.
'in the air' becomes 'ra' (I can't justify this - if you can you should give a lot more credence to this answer).
'force' becomes 'f' (symbol used in Physics e.g. f=ma).
'ra'+'f'='raf'
'raf' reversed gives 'FAR'.
'to' is the link.
Can you help me to learn more?
(Other definitions for far that I've seen before include "At a great distance way" , "Distant" , "Very much" , "Remote" , "A long, long way to go" .)