Men only name worker, not developing well (8)
I believe the answer is:
stagnant
'not developing well' is the definition.
Both the definition and answer are adjectives. Perhaps you can see an association between them that I don't see?
'men only name worker' is the wordplay.
'men only' becomes 'stag' (as in a stag do).
'name' becomes 'n' (common abbreviation e.g. on forms).
'worker' becomes 'ant' (worker is a type of ant).
'stag'+'n'+'ant'='STAGNANT'
Can you help me to learn more?
(Other definitions for stagnant that I've seen before include "Unmoving (water)" , "(Water) not flowing" , "Unhealthy from lack of movement" , "Showing little activity" , "Brackish and foul" .)