Perhaps Jack's getting marching orders? (5)
I believe the answer is:
cards
'marching orders?' is the definition.
(giving someone their cards or marching orders)
'perhaps jack's getting' is the wordplay.
'perhaps jack' becomes 'card' (type of playing card).
'getting' becomes 's' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'card'+'s'='CARDS'
Can you help me to learn more?
(Other definitions for cards that I've seen before include "Combs, cleans (raw wool); game" , "Birthday missives" , "Odd people" , "See 11" , "Get one's -----: it's a P45 nowadays!" .)