Beam securing more diseased ribbing (8)
I believe the answer is:
raillery
'diseased ribbing' is the definition.
Although both the answer and definition are singular nouns, I don't understand how they can define each other.
'beam securing more' is the wordplay.
'beam' becomes 'ray' (synonyms).
'securing' indicates putting letters inside.
'more' becomes 'iller' (I can't explain this - if you can you should believe this answer much more).
'ray' going around 'iller' is 'RAILLERY'.
Can you help me to learn more?
(Other definitions for raillery that I've seen before include "(Example of) banter" , "Light teasing repartee" , "Banter, back-chat" , "Good-humoured teasing" , "Satirical banter" .)