Prepare to fight back a lot (5)
I believe the answer is:
rearm
'prepare to fight' is the definition.
I can't judge whether this defines the answer.
'back a lot' is the wordplay.
'back' becomes 'rear' (something's rear is its back).
'a lot' becomes 'm' ().
'rear'+'m'='REARM'
Can you help me to learn more?
(Other definitions for rearm that I've seen before include "Take weapons again" , "Strengthen one's defences" , "Resupply with weapons" , "fit again" , "prepare for another war" .)