In the midst of a commotion, grand lady's holding fast (8)
I believe the answer is:
adhering
'holding fast' is the definition.
('adhere' can be a synonym of 'hold fast')
'in the midst of a commotion grand lady's' is the subsidiary indication.
'in the midst of' is an insertion indicator.
'commotion' becomes 'din' ('din' can be a synonym of 'commotion').
'grand' becomes 'g' ('G' can be a synonym of 'grand').
'lady' becomes 'her' (**).
'a'+'din'+'g'='ading'
'ading' enclosing 'her' is 'adhering'.
(Other definitions for adhering that I've seen before include "Sticking" , "holding fast" .)