heroin vs hard drug

heroin and hard drug both are nouns.

Word	Noun	Adjective	Verb	Adverb
heroin	Yes	No	No	No
hard drug	Yes	No	No	No

As nouns, hard drug is a hypernym of heroin; that is, hard drug is a word with a broader meaning than heroin:

heroin: a narcotic that is considered a hard drug; a highly addictive morphine derivative; intravenous injection provides the fastest and most intense rush
hard drug: a narcotic that is considered relatively strong and likely to cause addiction

Other hypernyms of heroin include opiate.

heroin (noun)	hard drug (noun)
a narcotic that is considered a hard drug; a highly addictive morphine derivative; intravenous injection provides the fastest and most intense rush	a narcotic that is considered relatively strong and likely to cause addiction