atomic weapon vs W.M.D.

atomic weapon and W.M.D. both are nouns.

Word	Noun	Adjective	Verb	Adverb
atomic weapon	Yes	No	No	No
W.M.D.	Yes	No	No	No

As nouns, W.M.D. is a hypernym of atomic weapon; that is, W.M.D. is a word with a broader meaning than atomic weapon:

atomic weapon: a weapon of mass destruction whose explosive power derives from a nuclear reaction
W.M.D.: a weapon that kills or injures civilian as well as military personnel (nuclear and chemical and biological weapons)

Other hypernyms of atomic weapon include weapon of mass destruction, WMD.

atomic weapon (noun)	W.M.D. (noun)
a weapon of mass destruction whose explosive power derives from a nuclear reaction	a weapon that kills or injures civilian as well as military personnel (nuclear and chemical and biological weapons)