Heavy field study (6)
I believe the answer is:
leaden
'heavy' is the definition.
(similar in meaning)
'field study' is the wordplay.
'field' becomes 'lea' (lea can mean a meadow or field of grass).
'study' becomes 'den' (term for a study or office).
'lea'+'den'='LEADEN'
(Other definitions for leaden that I've seen before include "Heavy - overcast" , "Heavy - plodding" , "Heavy or slow, like dark-gray metal" , "Dull, heavy, slow" , "Leaned over in slow, heavy way" .)