Stream of abuse from one stuck in traffic (6)
I believe the answer is:
tirade
'stream of abuse' is the definition.
(a tirade is an angry rant)
'one stuck in traffic' is the wordplay.
'one' becomes 'i' (Roman numeral).
'stuck in' means one lot of letters goes inside another.
'traffic' becomes 'trade' (traffic can mean illegal trade).
'i' put inside 'trade' is 'TIRADE'.
'from' acts as a link.
(Other definitions for tirade that I've seen before include "A long abusive harangue" , "Fulmination" , "Long speech of angry criticism" , "A long abusive denunciation" , "Speech of violent denunciation" .)