Lip-smacking snack? (7,8)
I believe the answer is:
knuckle sandwich
'lip-smacking snack?' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.
'smacking snack?' is the wordplay.
'smacking' becomes 'knuckle' (I am not sure about this - if you are sure you should believe this answer much more).
'snack?' becomes 'sandwich' (I've seen this before).
'knuckle'+'sandwich'='KNUCKLE SANDWICH'
Can you help me to learn more?
(Other definitions for knuckle sandwich that I've seen before include "Buffet" , "piece of pork between slices of bread" , "Punch in mug" , "Bunch of fives" , "hit" .)