atomic bomb vs A-bomb

atomic bomb and A-bomb both are nouns.

Word	Noun	Adjective	Verb	Adverb
atomic bomb	Yes	No	No	No
A-bomb	Yes	No	No	No

As nouns, atomic bomb and A-bomb are synonyms defined as:

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

atomic bomb (noun)	A-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)