Essentially, lunch ain't free (7)
I believe the answer is:
unchain
'free' is the definition.
(unchaining is a kind of freeing)
'essentially lunch ain't' is the wordplay.
'essentially' says the answer is hidden in the clue (essence can mean the inside of something).
'UNCHAIN' is hidden in the letters of 'lunch aint'.
(Other definitions for unchain that I've seen before include "Free" , "loose" , "Release from fetters" , "Release from bondage" .)