atom bomb vs clean bomb

atom bomb and clean bomb both are nouns.

Word	Noun	Adjective	Verb	Adverb
atom bomb	Yes	No	No	No
clean bomb	Yes	No	No	No

As nouns, clean bomb is a hyponym of atom bomb; that is, clean bomb is a word with a more specific, narrower meaning than atom bomb:

atom bomb: a nuclear weapon in which enormous energy is released by nuclear fission (splitting the nuclei of a heavy element like uranium 235 or plutonium 239)
clean bomb: an atom bomb leaving little or no radioactive contamination

Other hyponyms of atom bomb include dirty bomb, neutron bomb.

atom bomb (noun)	clean bomb (noun)
a nuclear weapon in which enormous energy is released by nuclear fission (splitting the nuclei of a heavy element like uranium 235 or plutonium 239)	an atom bomb leaving little or no radioactive contamination