Tread carelessly in business (5)
I believe the answer is:
trade
'business' is the definition.
(trade is a kind of business)
'tread carelessly' is the wordplay.
'carelessly' indicates an anagram.
'tread' is an anagram of 'TRADE'.
'in' is the link.
(Other definitions for trade that I've seen before include "Skilled occupation" , "A skilled craft to earn living" , "Buy and sell in business" , "Personal occupation" , "Dealing in goods" .)