Big name placed over new business (5-2)
I believe the answer is:
start up
'new business' is the definition.
(I've seen this before)
'big name placed over' is the wordplay.
'big name' becomes 'star' (I've seen this before).
'placed' becomes 'put' (I've seen this in other clues).
'over' is a reversal indicator.
'put' reversed gives 'tup'.
'star'+'tup'='START-UP'
(Other definitions for start up that I've seen before include "fresh concern" , "get going" , "Begin" , "Newly-established firm" , "Newly-formed company" .)