Above criticism, I do business (5)
I believe the answer is:
ideal
'above criticism' is the definition.
The answer and definition can be both related to thinking as well as being singular nouns.
Perhaps they are linked in a way I don't understand?
'i do business' is the wordplay.
'do business' becomes 'deal' (as in dealing with another business).
'i'+'deal'='IDEAL'
Can you help me to learn more?
(Other definitions for ideal that I've seen before include "Coal-mining waste" , "To which one aspires" , "The best conceivable" , "highly desirable" , "Utopian; yardstick" .)