One is seen in exchanges of invective (7)
I believe the answer is:
tirades
'invective' is the definition.
(I've seen this before)
'one is seen in exchanges' is the wordplay.
'one' becomes 'i' (Roman numeral).
'is seen in' is an insertion indicator.
'exchanges' becomes 'trades' (trade is a kind of exchange).
'i' placed inside 'trades' is 'TIRADES'.
'of' acts as a link.
(Other definitions for tirades that I've seen before include "Invective" , "It dares to unleash long angry speeches" , "Astride with streams of abuse" , "Denunciations" , "Rants" .)