Unwholesome number one and more than a couple (7)
I believe the answer is:
noisome
'unwholesome' is the definition.
(similar in meaning)
'number one and more than a couple' is the wordplay.
'number' becomes 'some' (I have seen 'Undefined number ' mean 'some' so perhaps 'number' could also mean 'some').
'one and' means one lot of letters go next to another.
'more than a couple' becomes 'noi' (I can't explain this - if you can you should believe this answer much more).
'some' put after 'noi' is 'NOISOME'.
Can you help me to learn more?
(Other definitions for noisome that I've seen before include "Evil-smelling, objectionable (7)" , "Nasty" , "Disagreeable, unpleasant" , "Obnoxious" , "Repugnant" .)