Harangue one entering business (6)
I believe the answer is:
tirade
'harangue' is the definition.
(I've seen this before)
'one entering business' is the wordplay.
'one' becomes 'i' (Roman numeral).
'entering' indicates putting letters inside.
'business' becomes 'trade' (trade is a kind of business).
'i' put inside 'trade' is 'TIRADE'.
(Other definitions for tirade that I've seen before include "Torrent of abuse" , "strong words" , "Speech of violent denunciation" , "Inclination; fish" , "A prolonged diatribe" .)