Display anti-aircraft gun, ignoring one order (4)
I believe the answer is:
pomp
'display' is the definition.
(both can mean ostentation or extravagance)
'anti-aircraft gun ignoring one order' is the wordplay.
I cannot quite see how this works, but
'order' could be 'po' and 'po' is located in the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for pomp that I've seen before include "Splendid ceremonial" , "Ceremonial grandeur" , "Vainglory" , "Ceremonial display" , "Stately display, goes with ceremony" .)