white pepper vs true pepper

white pepper and true pepper both are nouns.

Word	Noun	Adjective	Verb	Adverb
white pepper	Yes	No	No	No
true pepper	Yes	No	No	No

As nouns, true pepper is a hypernym of white pepper; that is, true pepper is a word with a broader meaning than white pepper:

white pepper: climber having dark red berries (peppercorns) when fully ripe; southern India and Sri Lanka; naturalized in northern Burma and Assam
true pepper: any of various shrubby vines of the genus Piper

Other hypernyms of white pepper include pepper vine.

white pepper (noun)	true pepper (noun)
pepper ground from husked peppercorns	any of various shrubby vines of the genus Piper
climber having dark red berries (peppercorns) when fully ripe; southern India and Sri Lanka; naturalized in northern Burma and Assam