Soldier: I quit legion (8)
I believe the answer is:
manifold
'legion' is the definition.
Although both the answer and definition are singular nouns, I can't see how one could define the other.
'soldier i quit' is the wordplay.
'soldier' becomes 'man' (man can mean a soldier).
'quit' becomes 'fold' (I can't explain this - if you can you should believe this answer much more).
'man'+'i'+'fold'='MANIFOLD'
Can you help me to learn more?
(Other definitions for manifold that I've seen before include "maths set" , "with several features" , "Chamber" , "performing several functions" , "having several different forms?" .)