Flourished cereal plate over head regularly (10)
I believe the answer is:
brandished
'flourished' is the definition.
('brandish' can be a synonym of 'flourish')
'cereal plate over head regularly' is the wordplay.
'cereal' becomes 'bran' (type of cereal).
'plate' becomes 'dish' (type of plate).
'over' means one lot of letters go next to another (in a down clue, some letters go over others).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
The alternating letters of 'head' are 'ed'.
'bran'+'dish'+'ed'='BRANDISHED'
(Other definitions for brandished that I've seen before include "Displayed" , "Waved" .)