Another business function fed by sandwich shop (8)
I believe the answer is:
sideline
'another business' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'function fed by sandwich shop' is the wordplay.
'function' becomes 'sine' (mathematical function).
'fed by' means one lot of letters goes inside another (one word is fed by another set of letters).
'sandwich shop' becomes 'deli' (short for delicatessen).
'sine' enclosing 'deli' is 'SIDELINE'.
Can you help me to learn more?
(Other definitions for sideline that I've seen before include "Boundary marker" , "hobby" , "Secondary job" , "Prevent from participating" , "not my main interest" .)