Dry — dull (4)
I believe the answer is:
arid
I believe this is a double definition.
'dry' is the first definition.
(similar in meaning)
'dull' is the second definition.
(I've seen this in another clue)
(Other definitions for arid that I've seen before include "(Of an area) very dry" , "Parched, waterless" , "Dry raid" , "Rainless (region)" , "Wadi may be this" .)