atomic weapon vs A-bomb

atomic weapon and A-bomb both are nouns.

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

As nouns, A-bomb is a hyponym of atomic weapon; that is, A-bomb is a word with a more specific, narrower meaning than atomic weapon:

atomic weapon: a weapon of mass destruction whose explosive power derives from a nuclear reaction
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)

atomic weapon (noun)	A-bomb (noun)
a weapon of mass destruction whose explosive power derives from a nuclear reaction	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)