Soldier one is not in favour of? (4)
I believe the answer is:
anti
'not in favour of?' is the definition.
(I've seen this before)
'soldier one' is the wordplay.
'soldier' becomes 'ant' (soldier is a type of ant).
'one' becomes 'i' (roman numeral).
'ant'+'i'='ANTI'
'is' is the link.
(Other definitions for anti that I've seen before include "One who is against (something)" , "Policy's opponent" , "Who pooh-poohs all" , "Prefix meaning against" , "Naysayer" .)