Boring do: suite horrible (7)
I believe the answer is:
tedious
'boring' is the definition.
(I know that boring can be written as tedious)
'do suite horrible' is the wordplay.
'horrible' indicates anagramming the letters.
'do'+'suite'='dosuite'
'dosuite' with letters rearranged gives 'TEDIOUS'.
(Other definitions for tedious that I've seen before include "Dull as ditchwater" , "drab" , "Humdrum" , "awfully boring" , "Long, slow, dull" .)