Prestige without end, so duke reflected (5)
I believe the answer is:
kudos
'prestige' is the definition.
(thesaurus)
'without end so duke reflected' is the wordplay.
'without end' means to remove the last letter.
'reflected' says the letters should be written backwards.
'so'+'duke'='soduke'
'soduke' with its last letter taken away is 'soduk'.
'soduk' in reverse letter order is 'KUDOS'.
(Other definitions for kudos that I've seen before include "Honour - cachet" , "Praise, honour" , "Laudation" , "Great prestige" , "Fame - prestige" .)