Very dry, or boring (4)
I believe the answer is:
arid
I believe this is a double definition.
'very dry' is the first definition.
(I've seen this before)
'boring' is the second definition.
(thesaurus)
(Other definitions for arid that I've seen before include "Parched with heat" , "Wadi may be this" , "Dry raid" , "Dry, devoid of interest" , "Excessively dry" .)