explosion vs big bang

explosion and big bang both are nouns.

Word	Noun	Adjective	Verb	Adverb
explosion	Yes	No	No	No
big bang	Yes	No	No	No

As nouns, big bang is a hyponym of explosion; that is, big bang is a word with a more specific, narrower meaning than explosion:

explosion: a violent release of energy caused by a chemical or nuclear reaction
big bang: (cosmology) the cosmic explosion that is hypothesized to have marked the origin of the universe

Other hyponyms of explosion include airburst, blast, backfire, backfire, blowback, fragmentation, inflation.

explosion (noun)	big bang (noun)
the act of exploding or bursting	(cosmology) the cosmic explosion that is hypothesized to have marked the origin of the universe
a golf shot from a bunker that typically moves sand as well as the golf ball
the terminal forced release of pressure built up during the occlusive phase of a stop consonant
a sudden outburst
a violent release of energy caused by a chemical or nuclear reaction
a sudden great increase
the noise caused by an explosion