Nun made ridiculously dull (7)
I believe the answer is:
mundane
'dull' is the definition.
(I've seen this before)
'nun made ridiculously' is the wordplay.
'ridiculously' indicates anagramming the letters.
'nun'+'made'='nunmade'
'nunmade' with letters rearranged gives 'MUNDANE'.
(Other definitions for mundane that I've seen before include "Earthly; unexciting" , "Banal; earthly" , "Unexciting; of this world" , "Everyday, humdrum" , "Ordinary, of this world" .)