Soldier on a separate base (9)
I believe the answer is:
persevere
'soldier on' is the definition.
(I've seen this before)
'a separate base' is the wordplay.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'separate' becomes 'sever' (sever can mean to split or separate).
'base' becomes 'e' (Euler's number - base of natural logarithms).
'per'+'sever'+'e'='PERSEVERE'
(Other definitions for persevere that I've seen before include "Press on" , "Struggle on!" , "Carry on regardless" , "Battle on" , "Continue - stick to one's guns" .)