Raise one in army (5)
I believe the answer is:
hoist
'raise' is the definition.
(hoisting is a kind of raising)
'one in army' is the wordplay.
'one' becomes 'i' (roman numeral).
'in' is an insertion indicator.
'army' becomes 'host' (host is a kind of army).
'i' placed into 'host' is 'HOIST'.
(Other definitions for hoist that I've seen before include "Lift, raise" , "group of flags" , "Substance forming outer skeleton of insects, etc" , "Device for lifting, often attached to 5 down" , "elevator" .)