One maybe seen on the box for a cake (4)
I believe the answer is:
soap
'a cake' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Perhaps you can see a link between them that I don't see?
'one maybe seen on the box' is the wordplay.
I cannot really understand how this works, but
'one' could be 'a' (a thing is one thing) and 'a' is located in the answer.
The remaining letters 'sop' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'for' is the link.
Can you help me to learn more?
(Other definitions for soap that I've seen before include "TV programme; cleanser" , "type of TV programme" , "Carbolic, perhaps" , "Cleaning substance - melodramatic TV or radio series" , "Cleansing bar" .)