Booze keeping US soldier lively (5)
I believe the answer is:
agile
'lively' is the definition.
(I've seen this in another clue)
'booze keeping us soldier' is the wordplay.
'booze' becomes 'ale' (type of alcohol).
'keeping' indicates putting letters inside (some letters kept inside).
'us soldier' becomes 'GI' (GI can mean an American soldier).
'ale' enclosing 'gi' is 'AGILE'.
(Other definitions for agile that I've seen before include "Nimble on the feet" , "Spry - energetic" , "Nimble, fleet" , "Limber" , "Lithely moving" .)