Feature expert in business paper (5)
I believe the answer is:
facet
'feature' is the definition.
(I know that facet is a type of feature)
'expert in business paper' is the wordplay.
'expert' becomes 'ace' (ace can informally mean very good).
'in' is an insertion indicator.
'business paper' becomes 'ft' (Financial Times newspaper).
'ace' put within 'ft' is 'FACET'.
(Other definitions for facet that I've seen before include "Smooth surface of a gem" , "side of rock" , "Small surface (of diamond)" , "Aspect or feature of something" , "Look" .)