In miners union one up against company in never-ending situation (9)
I believe the answer is:
continuum
'company in never-ending situation' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'in miners union one up against' is the wordplay.
'in' means one lot of letters goes inside another.
'miners' becomes 'co' (I can't explain this - if you can you should give a lot more credence to this answer).
'union' becomes 'NUM' (National Union of Mineworkers).
'one' becomes 'unit' (synonyms).
'up against' says the letters should be written in reverse.
'unit' backwards is 'tinu'.
'co'+'num'='conum'
'conum' enclosing 'tinu' is 'CONTINUUM'.
Can you help me to learn more?
(Other definitions for continuum that I've seen before include "Uninterrupted sequence" , "Unbroken series of indistinguishable parts" .)