In the army, you learn (4)
I believe the answer is:
hear
'learn' is the definition.
(I've seen this before)
'in the army you' is the wordplay.
'in' says the answer is hidden in the clue.
'HEAR' is hidden within 'the army you'.
(Other definitions for hear that I've seen before include "Listen to" , "Find out" , "Get wind of" , "attend" , "Pay attention" .)