Synonymous with The Big Bang and that's explosive (3)
I believe the answer is:
tnt
'that's explosive' is the definition.
(TNT is an example)
'synonymous with the big bang and' is the wordplay.
I cannot really see how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is found in the answer.
'and' could be 'n' (common abbreviation for 'and') and 'n' is located in the answer.
A single letter 't' remains which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for tnt that I've seen before include "Explosive compound" , "Explosive stuff" , "Type of high explosive" , "Very powerful explosive, compressed" , "Initially, powerful explosive" .)