fission bomb vs atomic bomb

fission bomb and atomic bomb both are nouns.

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

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

fission 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 fission bomb include A-bomb, atom bomb, plutonium bomb.

fission 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)