Mother returns for an instant with shells (4)
I believe the answer is:
ammo
'shells' is the definition.
(I've seen this in another clue)
'mother returns for an instant' is the wordplay.
'mother' becomes 'ma' (Ma is another word for mother or mum).
'returns' shows that the letters should be reversed in order.
'for' means one lot of letters go next to another.
'an instant' becomes 'mo'.
'ma' back-to-front is 'am'.
'am'+'mo'='AMMO'
'with' is the link.
(Other definitions for ammo that I've seen before include "Explosive devices" , "Shot" , "Bullets, shells, etc. (abbr.)" , "that goes in magazine: ...?" , "Slugs perhaps" .)