Works in Labour gaining superior ground
I believe the answer is:
topsoil
'ground' is the definition.
(I've seen this before)
'works in labour' is the wordplay.
'works' becomes 'ops' (op is short for opus, a work).
'in' means one lot of letters goes inside another.
'labour' becomes 'toil' (synonyms).
'ops' put into 'toil' is 'TOPSOIL'.
'gaining superior' acts as a link.
This may not be correct. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for topsoil that I've seen before include "surface of earth" , "best part of earth" , "Upper layer of earth" , "Visible layer of garden" , "Earth's surface" .)