I do business - thats perfect! (5)
I believe the answer is:
ideal
'perfect' is the definition.
(similar in meaning)
'i do business' is the wordplay.
'do business' becomes 'deal' (as in doing a business deal).
'i'+'deal'='IDEAL'
'thats' acts as a link.
(Other definitions for ideal that I've seen before include "Pattern" , "superb specimen" , "Model of excellence (5)." , "Conceptual" , "Model of excellance" .)