Explosive ingredient some disconcertingly brought round (5)
I believe the answer is:
nitre
'explosive ingredient' is the definition.
(I've seen this before)
'some disconcertingly brought round' is the wordplay.
'some' indicates a hidden word (some of the parts of the word are used).
'brought round' shows that the letters should be reversed in order.
'ertin' is hidden in the letters of 'disconcertingly'.
'ertin' reversed gives 'NITRE'.
(Other definitions for nitre that I've seen before include "explosive component" , "what goes into bangers" , "found in a slow match?" , "constituent of gunpowder" , "Inert (anag) - saltpetre" .)