Uproar as nonsense raised in initially serious meeting (5)
I believe the answer is:
storm
'uproar' is the definition.
(I've seen this before)
'nonsense raised in initially serious meeting' is the wordplay.
'nonsense' becomes 'rot' (I've seen this before**).
'raised' says the letters should be written backwards.
'in' indicates putting letters inside.
'initially' indicates taking the first letters.
The initial letters of 'serious meeting' is 'sm'.
'rot' reversed gives 'tor'.
'tor' placed into 'sm' is 'STORM'.
'as' acts as a link.
(Other definitions for storm that I've seen before include "Violent weather condition" , "violent reaction" , "Charge" , "Atmospheric disturbance, assault (stronghold)," , "commotion" .)