Long and nasty duel outside a broken-down bar (7)
I believe the answer is:
durable
'long' is the definition.
(similar in meaning)
'nasty duel outside a broken-down bar' is the wordplay.
'nasty' indicates anagramming the letters (a nasty or wrong spelling).
'outside' indicates putting letters inside (some letters go outside others).
'a broken down' indicates an anagram.
'duel' with letters rearranged gives 'dule'.
'bar' with letters rearranged gives 'rab'.
'dule' placed around 'rab' is 'DURABLE'.
'and' acts as a link.
(Other definitions for durable that I've seen before include "Lasting a long time" , "existing for a long time" , "Long-lasting and hard-wearing" , "Rugged; long-lasting" , "Firm" .)