pentazocine vs pain pill

pentazocine and pain pill both are nouns.

Word	Noun	Adjective	Verb	Adverb
pentazocine	Yes	No	No	No
pain pill	Yes	No	No	No

As nouns, pain pill is a hypernym of pentazocine; that is, pain pill is a word with a broader meaning than pentazocine:

pentazocine: analgesic drug (trade name Talwin) that is less addictive than morphine
pain pill: a medicine used to relieve pain

Other hypernyms of pentazocine include analgesic, anodyne, painkiller.

pentazocine (noun)	pain pill (noun)
analgesic drug (trade name Talwin) that is less addictive than morphine	a medicine used to relieve pain