Deal to contain one outburst (6)
I believe the answer is:
tirade
'outburst' is the definition.
(I've seen this before)
'deal to contain one' is the wordplay.
I cannot really understand how this works, but
'one' could be 'i' (Roman numeral) and 'i' is found within the answer.
'deal' could be 'trade' (synonyms) and 'trade' is present in the leftover letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tirade that I've seen before include "Prolonged abusive speech" , "Loud harangue" , "strong words" , "A long, abusive outburst" , "Sustained abuse" .)