atom bomb vs atomic bomb

atom bomb and atomic bomb both are nouns.

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

As nouns, atom bomb and atomic bomb are synonyms defined as:

atom bomb and atomic 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)

Other synonyms of atom bomb include A-bomb, fission bomb, plutonium bomb.

atom bomb (noun)	atomic 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)	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)