Dull, tedious (6)
I believe the answer is:
dreary
I believe this is a double definition.
'dull' is the first definition.
(similar in meaning)
'tedious' is the second definition.
(synonyms)
(Other definitions for dreary that I've seen before include "Grey and dull" , "Cheerless and dull" , "Monotonous" , "Dismal, funereal" , "Dismal, boring" .)