Though not so hostile, the West has to rearm frantically! (6)
I believe the answer is:
warmer
'though not so hostile' is the definition.
I can't judge whether this definition defines the answer.
'west has to rearm frantically' is the wordplay.
'west' becomes 'W' (abbreviation).
'has' means one lot of letters go next to another.
'frantically' indicates an anagram.
'rearm' anagrammed gives 'armer'.
'w'+'armer'='WARMER'
'the' acts as a link.
Can you help me to learn more?
(Other definitions for warmer that I've seen before include "Less cold" , "Containing more heat" , "Less cool" , "Having a higher temperature" , "Closer to target" .)