Half, nearly three quarters of words explosive (6)
I believe the answer is:
semtex
'words explosive' is the definition.
'semtex' can be an answer for 'explosive' (I've seen this before). I'm not certain of the 'words' bit.
'half nearly three quarters' is the wordplay.
'half' becomes 'semi' (I've seen this before).
'nearly' means to remove the last letter.
'three quarters' becomes 'tex' (I can't explain this - if you can you should believe this answer much more).
'semi' with its last letter taken away is 'sem'.
'sem'+'tex'='SEMTEX'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for semtex that I've seen before include "Plastic explosive from the Czech Republic" , "Explosive substance used by terrorists" , "Explosive material used by terrorists" , "Explosive commonly used by terrorists (6)" , "Type of plastic explosive" .)