Laboured conduct over discontented European (6)
I believe the answer is:
leaden
'laboured' is the definition.
(both can mean cumbersome or dull)
'conduct over discontented european' is the wordplay.
'conduct' becomes 'lean' (I can't explain this - if you can you should believe this answer much more).
'over' indicates putting letters inside.
'discontented' suggests removing the centre (the word's contents are removed).
'european' becomes 'dane' (someone from Denmark).
'dane' with its middle removed is 'de'.
'lean' enclosing 'de' is 'LEADEN'.
Can you help me to learn more?
(Other definitions for leaden that I've seen before include "Dull, heavy, slow" , "Heavy or slow, like dark-gray metal" , "Describes grey overcast skies" , "Leaned over in slow, heavy way" , "Gloomy - slow-moving" .)