atom bomb vs dirty bomb

atom bomb and dirty bomb both are nouns.

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

As nouns, dirty bomb is a hyponym of atom bomb; that is, dirty 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)
dirty bomb: an atom bomb that leaves considerable radioactive contamination

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

atom bomb (noun)	dirty 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 that leaves considerable radioactive contamination