Dull experts backing agency (7)
I believe the answer is:
prosaic
'dull' is the definition.
(similar in meaning)
'experts backing agency' is the wordplay.
'experts' becomes 'pros' (professionals).
'backing' says the letters should be written backwards.
'agency' becomes 'CIA' (CIA is an example).
'cia' back-to-front is 'aic'.
'pros'+'aic'='PROSAIC'
(Other definitions for prosaic that I've seen before include "Pedestrian, unimaginative" , "Poetry would not be so" , "Humdrum" , "Non-poetic, unromantic" , "Matter-of-fact" .)