Hot air, perhaps, as a line in business (6)
I believe the answer is:
tirade
'hot air perhaps' is the definition.
I can't judge whether this defines the answer.
'a line in business' is the wordplay.
'a line' becomes 'i' (I can't justify this - if you can you should believe this answer much more).
'in' means one lot of letters goes inside another.
'business' becomes 'trade' (trade is a kind of business).
'i' inserted inside 'trade' is 'TIRADE'.
'as' is the link.
Can you help me to learn more?
(Other definitions for tirade that I've seen before include "Long, abusive speech" , "A long abusive denunciation" , "A long abusive harangue" , "Loud harangue" , "A prolonged outburst of angry words" .)