Illicit affairs of spymaster running major industry (6,8)
'illicit affairs' is the definition.
'spymaster running major industry' is the wordplay.
'spymaster' becomes 'm' (in James Bond).
'running' becomes 'on' (I've seen this in other clues).
'major' becomes 'key'.
'industry' becomes 'business'.
'm'+'on'+'key'+'business'='MONKEY BUSINESS'
'of' acts as a link.
(Other definitions for monkey business that I've seen before include "Mischievous behaviour" , "fiddle" , "Marx Brothers film" , "may be amusingly projected" , "larking about" .)
'illicit affairs' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.
'spymaster running major industry' is the wordplay.
'spymaster' becomes 'm' (in James Bond).
'running' becomes 'on' (I've seen this in other clues).
'major industry' becomes 'key' (I can't explain this - if you can you should believe this answer much more).
'm'+'on'+'key'='MONKEY'
'of' acts as a link.
(Other definitions for monkey that I've seen before include "Medium-sized primate" , "Type of wrench for a monkey" , "Araucaria -- evergreen conifer" , "Long-tailed primate" , "Any of various long-tailed primates" .)