nuclear weapon vs WMD

nuclear weapon and WMD both are nouns.

Word	Noun	Adjective	Verb	Adverb
nuclear weapon	Yes	No	No	No
WMD	Yes	No	No	No

As nouns, WMD is a hypernym of nuclear weapon; that is, WMD is a word with a broader meaning than nuclear weapon:

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

Other hypernyms of nuclear weapon include W.M.D., weapon of mass destruction.

nuclear weapon (noun)	WMD (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)