A mob that's only half heartedly productive (6)
I believe the answer is:
arable
'productive' is the definition.
(similar in meaning)
'a mob that's only half heartedly' is the wordplay.
'mob' becomes 'rabble' (synonyms).
'that's only half' means to take half the letters.
'heartedly' becomes 'le' (I can't justify this - if you can you should believe this answer much more).
'rabble' cut in half is 'rab'.
'a'+'rab'+'le'='ARABLE'
Can you help me to learn more?
(Other definitions for arable that I've seen before include "Fit for crop growing" , "like "The Fields"?" , "(Of land) able to be cultivated" , "Such land is fit for tillage" , "Of land, capable of growing crops" .)