The invective when I swap round! (6)
I believe the answer is:
tirade
'the invective' is the definition.
(thesaurus)
'i swap round' is the wordplay.
'swap' becomes 'trade' (synonyms).
'round' means one lot of letters goes inside another.
'i' inserted within 'trade' is 'TIRADE'.
'when' acts as a link.
(Other definitions for tirade that I've seen before include "Flow of invective" , "String of invective" , "strong words" , "A prolonged outburst of angry words" , "Verbal broadside" .)