Smart, which is auspicious (6)
I believe the answer is:
bright
This clue is a double definition.
'smart' is the first definition.
(synonyms)
'auspicious' is the second definition.
(thesaurus)
'which is' acts as a link.
(Other definitions for bright that I've seen before include "Shining; intelligent" , "full of promise" , "Vivid - promising - smart" , "Mentally quick or radiating light" , "Cheerful or quick-witted" .)