Rationalise current business (10)
I believe the answer is:
streamline
'rationalise' is the definition.
(streamline can mean to make more rational)
'current business' is the wordplay.
'current' becomes 'stream' (synonyms).
'business' becomes 'line' (as in someone's line of work).
'stream'+'line'='STREAMLINE'
(Other definitions for streamline that I've seen before include "Get more efficient" , "eliminate resistance" , "Make (a body) less resistant to fluid flow" , "Improve efficiency" , "run things more efficiently" .)