Strange idea for upstart Parisian's farewell (5)
I believe the answer is:
adieu
'parisian's farewell' is the definition.
(I've seen this in another clue)
'strange idea for upstart' is the wordplay.
'strange' indicates an anagram.
'for' says to put letters next to each other.
'upstart' becomes 'u' (start of the word 'up').
'idea' with letters rearranged gives 'adie'.
'adie'+'u'='ADIEU'
(Other definitions for adieu that I've seen before include "Farewel" , "All the best" , "A valediction" , "Vale" , "cheers" .)