Convened in an auspicious atmosphere (3)
I believe the answer is:
sat
'convened' is the definition.
(sitting is a kind of convening)
'in an auspicious atmosphere' is the wordplay.
'in' says the answer is hidden in the clue.
'SAT' is hidden in the letters of 'auspicious atmosphere'.
(Other definitions for sat that I've seen before include "Took (an exam)" , "Was couch potato" , "Posed (for an artist)" , "Used a chair" , "Relaxed" .)