purple heart vs barbiturate

purple heart and barbiturate both are nouns.

Word	Noun	Adjective	Verb	Adverb
purple heart	Yes	No	No	No
barbiturate	Yes	No	No	No

As nouns, barbiturate is a hypernym of purple heart; that is, barbiturate is a word with a broader meaning than purple heart:

purple heart: a long-acting barbiturate used as a sedative
barbiturate: organic compound having powerful soporific effect; overdose can be fatal

purple heart (noun)	barbiturate (noun)
a long-acting barbiturate used as a sedative	organic compound having powerful soporific effect; overdose can be fatal