British commercial rubbish (3)
I believe the answer is:
bad
'rubbish' is the definition.
Although both the answer and definition are singular nouns, I cannot see how they can define each other.
'british commercial' is the wordplay.
'british' becomes 'b' (abbreviation e.g. in 'BBC').
'commercial' becomes 'ad' (abbreviation for advertisement).
'b'+'ad'='BAD'
Can you help me to learn more?
(Other definitions for bad that I've seen before include "Severe; of low standard" , "(Of food) decayed" , "Wicked" , "Evil, below standard or off" , "Stinking" .)