Give a lift to one in the army (5)
I believe the answer is:
hoist
'give a lift to' is the definition.
(I've seen this before)
'one in the army' is the wordplay.
'one' becomes 'i' (Roman numeral).
'in the' means one lot of letters goes inside another.
'army' becomes 'host' (host is a kind of army).
'i' put inside 'host' is 'HOIST'.
(Other definitions for hoist that I've seen before include "piece of lifting gear" , "Device for lifting, often attached to 5 down" , "(Equipment for) lift(ing)" , "Raise on pulleys" , "Lift using pulley and ropes" .)