In the main, one may use this item, roughly cutting bread (7,3)
I believe the answer is:
bathing cap
'in the main one may use this item roughly cutting bread' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Perhaps you can see an association between them that I can't see?
'item roughly cutting bread' is the wordplay.
'item' becomes 'thing' (both can mean an object).
'roughly' becomes 'ca' (abbreviation for circa).
'cutting' is an insertion indicator (some letters cut their way into a word).
'bread' becomes 'bap' (I can't explain this - if you can you should give a lot more credence to this answer).
'thing'+'ca'='thingca'
'thingca' placed into 'bap' is 'BATHING-CAP'.
Can you help me to learn more?
(Another definition for bathing cap that I've seen is " Swimmer's hair protector".)