Gold rush could be magnificent (6)
I believe the answer is:
august
'be magnificent' is the definition.
(thesaurus)
'gold rush' is the wordplay.
'gold' becomes 'au' (Au is the chemical symbol for gold).
'rush' becomes 'gust' (I have seen 'Rush of wind ' mean 'gust' so perhaps 'rush' could also mean 'gust').
'au'+'gust'='AUGUST'
'could' acts as a link.
(Other definitions for august that I've seen before include "Inspiring respect; month" , "Dignified - time of year" , "For Edna O'Brien, it was a 27 across month" , "Month befitting a lord" , "when students are down?" .)