Explosive device in list written down the wrong way (9)
I believe the answer is:
detonator
'explosive device' is the definition.
(detonator is a kind of explosive device)
'list written down the wrong way' is the wordplay.
'list' becomes 'rota' (rota is a kind of list).
'written down' becomes 'noted' (noting is a kind of writing down).
'the wrong way' says the letters should be written backwards.
'rota'+'noted'='rotanoted'
'rotanoted' back-to-front is 'DETONATOR'.
'in' acts as a link.
(Other definitions for detonator that I've seen before include "One sets off bang" , "means to cause explosion" , "That has explosive effect" , "small charge" , "Device for setting off a bomb" .)