Dangerous device on a street makes one rant (7)
I believe the answer is:
bombast
'one rant' is the definition.
(synonyms)
'dangerous device on a street' is the wordplay.
'dangerous device' becomes 'bomb' (explosive).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'street' becomes 'st' (abbreviation).
'bomb'+'a'+'st'='BOMBAST'
'makes' is the link.
(Other definitions for bombast that I've seen before include "High-flown language" , "Pompous talk" , "hollow material" , "Pomposity" , "High-sounding words with little meaning" .)