Explosive stuff seen in magazine? (9)
I believe the answer is:
gunpowder
'explosive stuff' is the definition.
'gunpowder' can be an answer for 'stuff' (gunpowder is a kind of stuff). I'm not sure about the 'explosive' bit.
'seen in magazine?' is the wordplay.
'seen in' becomes 'gun' (I can't justify this - if you can you should believe this answer much more).
'magazine?' becomes 'powder' (synonyms).
'gun'+'powder'='GUNPOWDER'
Can you help me to learn more?
(Other definitions for gunpowder that I've seen before include "plot? Sort of" , "this plot failed" , "Explosive invented in 9th-century China" , "Explosive mixture - plot of 1605" , "and 24: 1605 conspiracy" .)