Polish overheard that submarine, say (8)
I believe the answer is:
sandwich
'that submarine say' is the definition.
(submarine is a kind of sandwich)
'polish overheard' is the wordplay.
'polish' becomes 'sand' (to polish or sand down).
'overheard' becomes 'wich' (I can't explain this - if you can you should give a lot more credence to this answer).
'sand'+'wich'='SANDWICH'
Can you help me to learn more?
(Other definitions for sandwich that I've seen before include "The snack might result in bad chin wads" , "Double-decker, perhaps" , "Filled sponge cake" , "The snack makes strange chin wads" , "Food between slices" .)