Dreary field study (6)
I believe the answer is:
leaden
'dreary' is the definition.
(thesaurus)
'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 "Slow-moving, being like heavy metal" , "Oppressive" , "Describes grey overcast skies" , "Depressing - heavy" , "Dull, heavy, slow" .)