junky vs heroin addict

junky and heroin addict both are nouns.

Word	Noun	Adjective	Verb	Adverb
junky	Yes	No	No	No
heroin addict	Yes	No	No	No

As nouns, heroin addict is a hyponym of junky; that is, heroin addict is a word with a more specific, narrower meaning than junky:

Other hyponyms of junky include cocaine addict, binger, crack addict, opium addict, opium taker, withdrawer.

junky (noun)	heroin addict (noun)
a narcotics addict	someone addicted to heroin
someone who is so ardently devoted to something that it resembles an addiction