Explosive compound (7)
'explosive compound' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for tnt that I've seen before include "Explosive compound" , "Explosive stuff" , "Type of high explosive" , "Initially, powerful explosive" , "Very powerful explosive, compressed" .)
(Other definitions for nitrate that I've seen before include "salt" , "Fertiliser chemical" , "Tear tin up for fertiliser" , "Nattier (anag.)" , "Natural or synthetic fertiliser" .)