Dull field study (6)

I believe the answer is:

leaden

'dull' is the definition.
(I've seen this before)

'field study' is the wordplay.
'field' becomes 'lea' (I've seen this before).
'study' becomes 'den' (I've seen this before).
'lea'+'den'='LEADEN'

(Other definitions for leaden that I've seen before include "Describes grey overcast skies" , "Oppressive" , "Heavy or slow, like dark-gray metal" , "Dull, heavy, slow" , "Gloomy - slow-moving" .)

I've seen this clue in The Times.

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