Treat badly though not fit to employ (6)
I believe the answer is:
illuse
'not fit to employ' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'treat badly' is the wordplay.
I cannot quite see how this works, but
'treat' could be 'use' (using is a kind of treating) and 'use' is located in the answer.
'badly' could be 'ill' (eg in ill-advised) and 'ill' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
'though' is the link.
Can you help me to learn more?
(Another definition for illuse that I've seen is " Punishment".)